Cavity Wall Construction

PW999

I have been a long time reader of this forum and have obtained some valuable information to-date. Now I would appreciate some insight/opinions.

We finally received planning permission for an exposed site in west of Ireland (2 story house, brick construction, approx. 3,000 ft2) . Our architect is recommending 450mm call construction based on the denby dale passiv house with pumped insulation. We have reservations about this method as the architect is only just in the process of building one house using these methods at the moment.

We are not going for full passive house due to the views being mostly north facing and the wishes to have turf burning stoves and the total costs involved.

Family members who are involved in building trade (I have no knowledge at all apart from Boards !!!) and who will be overseeing the build have raised concerns over this building method, preferring the more traditional building methods of 100 to 150 mm cavity wall with 60mm or 80mm kingspan insulation with the walls drylined with additional 60/80mm insulation. They are raising concerns that the walls need to able breath, there should be air gap in the cavity and that they has seen endless problems with pumped insulation. I know the developments with the increased use of these products will probably eliminate some of the horror stories, however we are undecided as to whether to go with the new methods or the traditional tried and tested methods.

We have spoken to our engineer and he has only designed the one house in this manner which is only at roof level. He did have reservations about this build method but will the advancements in wall ties he is happy that this can be structurally achievable.

We are in the process of preparing detailed tender documents and having the engineer prepare the raft/wall/but the project is on hold until we decide on the wall construction.

We will be going for HRV, airthght finish with triple glazed windows. Due to land probably not going for geothermal. Will probably go for solar for hot water, stoves for heat and gas/oil condensing boiler for any additional heating needs.

Any insights appreciated.

just do it

PW999 wrote: »

they has seen endless problems with pumped insulation.

What kind of problems do they mean? I find it hard to see how insulation boards can be better.

fclauson

I would suggest before you do anything you get someone to help you do a PHPP calculation - even you arch might do this as there have been a number of free courses to get people educated

I did - and probably will now go for a 350mm wall using a full fill board system (100m block/150 full fill board/100 block) - I was going 450mm but there are issues with cills, lintels, how to hang windows, cavity closures - all of which are not insurmountable but need addressing (more expensive due to more footings, more expensive wall ties, unusual detailing which a builder might not be familiar with etc) and at 350mm I can get 0.136 U - which is good.

On the heating side - determine the demand before you determine the type.

Airtight/Insulate/ventilate – then worry about the rest

My current demand is down to 19.9 Kwh/M2/Annum and will probably be an A2 – and at a cost which is not much more than a regular build.

RKQ

just do it wrote: »

What kind of problems do they mean? I find it hard to see how insulation boards can be better.

A clear cavity of even 40mm will stop water crossing the cavity, especially in a porous brick wall. Water will penetrate a brick wall. Thats why the cavity wall has become a traditional method of building in our mild, damp, wind driven rain climate.

Personally I welcome new methods of building. External insulation seems to work well with Passive houses. I have never been a fan of cavity fill, as much can depend on the installer on the day.

Google same for info on faults or problems with cavity fill. There have been problems with full cavity fill in the UK.

There are many Passivhaus buildings in Ireland. Investigate same, maybe visit some and speak to the homeowners. Get lots of feedback. It will be important that you decide on a construction method based on your study and go from there.

beyondpassive

On the heating side - determine the demand before you determine the type[/COLOR]
[/Quote]

Well said FC

I'm a fan of the system of using taped PIR board in the cavity and have done this with an 80+60mm boards with staggered and taped joints. However it has an equal number of challenges to bead filled wide cavity. Such as sequencing of works with outer leaf built to follow each insulation board course, the voiding of warranties for non standard details. How you place and seal the window is an issue no matter what low energy solution you select and a 30mm drained cavity is needed minimum when taped Pir board is used so this brings the cavity to 170mm plus.

The best way to select the wall system, is to get straight into the detail. One self builder I know, mocked up parts of the building to see how the issues are solved. Easier done on the drawing board but the proof of the pudding is in the eating.

therightangle

PW999 wrote: »

"exposed site" "west of Ireland" "brick construction"
Our architect is recommending ...... pumped insulation

Will he certify that build?
Are you sure its an exposed brick finish?
Or do you mean "block construction"?

PW999

thanks for the replies

therightangle wrote: »

Will he certify that build?
Are you sure its an exposed brick finish?
Or do you mean "block construction"?

Sorry this should have been block construction.

just do it wrote: »

What kind of problems do they mean? I find it hard to see how insulation boards can be better.

Just Do It- the problems that have been told to us is primarily dampness within the house which has been caused through either poor installation or inferior quality materials being used. I guess this can be counteracted by using reputable suppliers and through thermal imagining. As family members will be supervising the build we don't have the same concerns with insulation boards.

With the 250mm cavity which is being proposed, we have concerns with the driving rain/wind and the fact that we haven't been able to speak to anyone who has this currently in their house. This is supported by some contractors we have spoken to who actually are saying that a map may be produced in the near future highlighting where pumped insulation is suitable.

[

QUOTE=fclauson;72993336]I would suggest before you do anything you get someone to help you do a PHPP calculation - even you arch might do this as there have been a number of free courses to get people educated

Getting onto the architect to get these calculations

therightangle

PW999 wrote: »

With the 250mm cavity which is being proposed, we have concerns with the driving rain/wind and the fact that we haven't been able to speak to anyone who has this currently in their house. This is supported by some contractors we have spoken to who actually are saying that a map may be produced in the near future highlighting where pumped insulation is suitable.

Do a google search for "IAB" and the name of the bead that you intend using - chances are you will find the IAB easily and in that you should see a map of where it is/isnt suitable to use it without a render protection, if thats the map you mean.

beyondpassive

The bonded bead in the cavity, does not inhibit moisture from draining down through the cavity, the beads have gaps that allow any water that may get into the cavity to find their way out. Vapour pressure is outwards for most of the year (all but about 3 weeks in most places) to push the dew point to the ouside of the cavity and cavity trays sloping outwards over lintols, under cills and at base of cavity ensure any water that gets through will be deflected outwards.

Worth noting that the enhanced quality control of a low energy airtight house, means that seals and flashings are applied to a high standard.

PM me for details of wide cavity. If your not thermally breaking the innerleaf where it sits on the rising wall or raft, then probably no point me sending you the detail.

rural_red

I have designed a few houses using the more 'traditional' partial filled 100mm cavity with insulated drylining. This method is generally not going to get you a Passiv Haus equivalent U value without deep drylining insulation. This presents its own problems as you will generally place an airtight layer/vapour control close to the inner leaf of the blockwork to allow for a service cavity closer to the interior. Doing this encourages interstitial condensation. Not doing this endangers the viability of the airtightness layer as trades get onto first fix etc. This is one concern but it can be overcome to a certain extent by using breathable insulation such as soy/hemp/wool or similar within the drylining.

In terms of the wide cavity solution this means wider rising walls, wider foundations, wider cills, wider lintols, proprietary cavity closers which all add expense while still leaving you with the worry of not having a sacrificial outer leaf with some sort of cavity.

Bonded bead will have holes but no one knows what direction rainwater will take across the cavity in extreme conditions. Water Vapour is one thing, liquid water is quite another thing. I would also be worried about this method.

If you are intent on Passuv Haus equivalent performance appropriate for driving rain I personally would consider sonething totally different....maybe and as one post already said, you should look at external insulation over a monolithic block wall with a rainscreen to the outside?

Utimately I d ask the following questions of your Architect;

1. What are the additional costs re structure for a wide cavity?

2. Can he/she be sure that water will not bridge the filled cavity?

3. If the bonded bead is wet will it still maintain its thermal properties?

just do it

rural_red wrote: »

you should look at external insulation over a monolithic block wall with a rainscreen to the outside

With EWI, how confident are you driving rain won't penetrate?

sas

just do it wrote: »

With EWI, how confident are you driving rain won't penetrate?

Given that he specifically suggested a rain screen to the outside he can't be terribly confident.

insulation monkey

Hi all,
I have heard all the cowboy stories and all the ways of doing it wrong, but can someone explain simply layer by layer how to correctly dry line using kingspan insulated plasterboard,the inside of a solid block or stone property to avoid mould\condensation.

Thanks.

beyondpassive

rural_red wrote: »

Utimately I d ask the following questions of your Architect;

1. What are the additional costs re structure for a wide cavity?

2. Can he/she be sure that water will not bridge the filled cavity?

3. If the bonded bead is wet will it still maintain its thermal properties?

1. for 150mm, virtually no extra cost, for 250mm, wall ties go to stainless steel deep profile and the window reveal is different to standard, the rising wall can have more block as it is 450mm wide and you are thermally breaking the inner leaf with Autoclaved Aerated block (*kept dry above DPC). Not hugely significant, though in overall cost terms.

2 I know how insidious the Western rains are, but with both hydrothermal analyis and annecdotal evidence from partial demolition of walls in cavities in Mayo, this isnt such an issue. Most dampness that occurs inside buildings is due to condensation forming on cold bridges or the coldest unvented spots on the walls. The background ventilation in the west is incredibly high (making it ideal for MHRV which lowers humidity). Moisture will penetrate the sand cement render but will not migrate through the block, water vapour always moves to the cold side, and both gravity capillary action of the huge surface area of the insside of a block, fights against the water being soaked by the block. Most important is to keep the block and cavities clean and the DPC's tidy.

Fill a drum with bonded bead next time you visit the insulation supplier, drill a hole in the bottom, pour in a litre, collect the water, measure after an hour, tel us what you get?

3. The bonded bead wouldnt get wet unless you had failure of 2 or more elements, such as DPC and render or silicon seals, any water vapour that gets in, would be pushed back out as water vapour wants in equalise with low pressure air which equates to low temperature or lower humidity air.(except for maybe 2 weeks in summer when temperatures are over 18 vapour pressure moves inwards, dosen't look like happening this summer :-), vapour back diffusion membranes use this concept).

Got the opertunity to try Fclausons software which integrated PHPP and DEAP, and outputs annual running costs. Very impressed with it and to my surprise the PHPP and DEAP energy demands pretty much corresponded once we added solar thermal to comply with Part L 2008.

insulation monkey wrote: »

Hi all,
I have heard all the cowboy stories and all the ways of doing it wrong, but can someone explain simply layer by layer how to correctly dry line using kingspan insulated plasterboard,the inside of a solid block or stone property to avoid mould\condensation.

Thanks.

PIR board glued to wall, back diffusion permiable vapour control layer (VCL), plasterboard, all pipes and electrical penetrations sealed where they puncture the VCL

galwaytt

PW999 wrote: »

We finally received planning permission for an exposed site in west of Ireland (2 story house, brick construction, approx. 3,000 ft2) ........
Family members who are involved in building trade ...... They are raising concerns that .... there should be air gap in the cavity

We have spoken to our engineer and he has only designed the one house in this manner which is only at roof level. He did have reservations about this build method but will the advancements in wall ties he is happy that this can be structurally achievable.

therightangle wrote: »

Will he certify that build?
Are you sure its an exposed brick finish?
Or do you mean "block construction"?

A West resident myself, I'm curious that you have PP for any kind of brick construction. Is it actually 'brick' - or do you mean concrete block? In Galway, it has long fallen out of favour with planners, and out of favour with engineers over water ingress. The West is just too wet.

Indeed, when I built my first house, in 1993, with a brick facade to front, the engineer even then said he would not certify any brick in the chimney construction, full-stop, over water ingress.

Outside of that, you're telling us that the advice to build this way, is from someone who hasn't built a finished building that way yet. If you're happy to be a test case, and you have confidence, great. I would concur with your family members though - the West of Ireland demands a clear cavity for water 'management'.

As for the extra-wide cavity model - who's standing over it, and the ties. I know one architect and he won't stand over anything over 120mm. YMMV and all that.

just do it

galwaytt wrote: »

I would concur with your family members though - the West of Ireland demands a clear cavity for water 'management'.

So what about all the partial fill cavities that have been pumped and are now full fill? Do you think this is going to cause problems in the long run?

Poor Uncle Tom

just do it wrote: »

So what about all the partial fill cavities that have been pumped and are now full fill? Do you think this is going to cause problems in the long run?

That depends on whether you think dampness will cross a narrow strip of beaded insulation and then make it's way through some board insulation to the inside leaf. Then it's a case of whether enough dampness can do this to make a sufficient mark on the inside leaf to appear on the inside of the building. In most cases I don't believe it would be enough to mark the inside of the wall, but that does not mean it is not getting to the inside leaf in small quantities.

The bigger issue with completeing the cavity fill from partial to full is that filling a narrow gap is harder to do and there will always be the areas youo can't reach. At least that's my perception of it.

tuggers

its never good to have insulation in the cavity and on the inside wall aswell
just browsing the site

just do it

Poor Uncle Tom wrote: »

That depends on whether you think dampness will cross a narrow strip of beaded insulation and then make it's way through some board insulation to the inside leaf. Then it's a case of whether enough dampness can do this to make a sufficient mark on the inside leaf to appear on the inside of the building. In most cases I don't believe it would be enough to mark the inside of the wall, but that does not mean it is not getting to the inside leaf in small quantities.

The bigger issue with completeing the cavity fill from partial to full is that filling a narrow gap is harder to do and there will always be the areas youo can't reach. At least that's my perception of it.

Thanks PUT
Following on from this it's hard to see the justification of a partial fill in the first place. The context here is exposed sites on the western coast line.

So if building in such a location using wide cavity construction (200-250mm), proper placing of wall ties (slanted outwards), clean cavity, use of cavity trays particularly on the SW walls, one should be confident water won't penetrate the inner leaf.

Anyone disagree?

just do it

tuggers wrote: »

its never good to have insulation in the cavity and on the inside wall aswell
just browsing the site

Welcome!
The boards PUT refer to are within the cavity rather than internal drylining.

Poor Uncle Tom

just do it wrote: »

So if building in such a location using wide cavity construction (200-250mm), proper placing of wall ties (slanted outwards), clean cavity, use of cavity trays particularly on the SW walls, one should be confident water won't penetrate the inner leaf.

I'd agree with that.

Slig

There are a few companies that do full fill cavity boards now, they are aeroboard or aeroboard with a PIR backing board which IMO is far more suitable for use in a potentially damp cavity than PIR alone. The outside face of the boards is corrugated to keep a 10mm drainage cavity should moisture penetrate the outer leaf of blockwork and the external render. They are tongue and groove giving a more permanent seal then taped butt joints and can be joined at corners with proprietry corner pieces or simply glued together.

It would allow far more quality control than pumping the cavity while still giving a respectable level of insulation.

sinnerboy

Look at the table at the top of page 2 here

I would love to get a blockies take on this.

A 100mm block may be between 103mm and 95mm. And they are laid off ( often wobbly) scaffolding more often than not in wet cold windy and conditions. I have seen wide variations in clear cavity widths i.e. 75mm cavity narrowing to 60mm or up to 90mm. No kidding. Over and over again over 26 years. Keep this to the forefront of your mind if attempting to use full fill boards.

just do it

sinnerboy wrote: »

Look at the table at the top of page 2 here

I would love to get a blockies take on this.

A 100mm block may be between 103mm and 95mm. And they are laid off ( often wobbly) scaffolding more often than not in wet cold windy and conditions. I have seen wide variations in clear cavity widths i.e. 75mm cavity narrowing to 60mm or up to 90mm. No kidding. Over and over again over 26 years. Keep this to the forefront of your mind if attempting to use full fill boards.

Yes very valid. A wide cavity with full fill done well should get over these differences. First and foremost though is quality of materials and workmanship!

sinnerboy

just do it wrote: »

First and foremost though is quality of materials and workmanship!

And understanding and appreciating the inevitable shortfalls

galwaytt

sinnerboy wrote: »

... And they are laid off ( often wobbly) scaffolding more often than not in wet cold windy and conditions. ....

Slig wrote: »

... and can be joined at corners with proprietry corner pieces or simply glued together.

Taking sinnerboy's comment above (which btdt, btw), I cannot see how, correction: I would love to see how, in the same wet/wind/wobbly (hold on: is that the new www ? ) anyone will cut, join, tape or glue a wet board, in a cavity.

When blocklayers have been using their trowel edges as knives for boards til now, are we saying they're all going to 'change gear' now...and cut mm-square, and seal the cut.....?....[wonders........]

Fine in the lab, but not out 'in the field' (sic). When

Slig

Unfortunately these things will have to change. If I see someone on one of my sites taking shortcust they get to try it all again properly. There is no excuse for piss poor workmanship especially now when anyone can be replaced. If you are happy with a "this is the way I've always done it" builder then good luck but most of my clients are now realising the advantages of building properly.

To get better results unfortunately you need to be precise, Air tightness, thermally broken materials, passive haus technology. These are all advances that require careful detailing and its the way things are going.

The reason I like the cavity fill board system is that it seems to be fool proof. There is less work than taping joints in PIR boards and ensuring there is a clear 40mm cavity. The boards are T&G and sized to correspond with the blockwork and if the inner leaf is built 1 course higher than the outer leaf the outer leaf can just be fitted tight against the outer face of the insulation. The boards themselves are polystyrene bead based and although they are much less effecient than PIR they wont degrade in the damp or desintegrate if they get rained on while the wall is being built. Its a compromise in performance to allow for an easier build.

galwaytt

Slig wrote: »

Unfortunately these things will have to change. If I see someone on one of my sites taking shortcust they get to try it all again properly. There is no excuse for piss poor workmanship especially now when anyone can be replaced. If you are happy with a "this is the way I've always done it" builder then good luck but most of my clients are now realising the advantages of building properly.

To get better results unfortunately you need to be precise, Air tightness, thermally broken materials, passive haus technology. These are all advances that require careful detailing and its the way things are going.

The reason I like the cavity fill board system is that it seems to be fool proof. There is less work than taping joints in PIR boards and ensuring there is a clear 40mm cavity. The boards are T&G and sized to correspond with the blockwork and if the inner leaf is built 1 course higher than the outer leaf the outer leaf can just be fitted tight against the outer face of the insulation. The boards themselves are polystyrene bead based and although they are much less effecient than PIR they wont degrade in the damp or desintegrate if they get rained on while the wall is being built. Its a compromise in performance to allow for an easier build.

I agree with all you've said, but that's not the point I was making. It isn't even about taking shortcuts: the point I was making is, is it possible, or reasonable, to expect those levels of quality onsite, in a real-world Irish climate situation ? There are real issues of wind, water, and access, to deal with.

This is one reason why a pumped, full-fill cavity is attractive - it's just plain easier. Like anything on-site, in life even, if it's easier to do it well, it's more likely to be done well in the first place. If, on the other hand, it's more difficult..........ymmv as they say !

Have you ever tried to bond wet insulation ? I have ......and it doesn't work.

To get good results needs good workmanship, good materials, but also a practical approach to what's achievable. Passive house brings that as a necessity, but you don't to, or shouldn't need to build to Passive, to get good quality. Quality is not the sole preseve of PHI.

As for materials, well for that reason too, choosing EPS/XPS in any form is not a compromise at all - rather the opposite in fact, if it delivers better (i.e. achievable) quality, more easily.

Slig

For me the cavity fill boards are the best compromise as they "should" be easy to install correctly.

A house should be built to last, otherwise whats the point. If the weather conditions on a particular day arent suitable for doing the job correctly then the job should be put off until the weather is better. There is no point ploughing ahead sticking wet boards together while its lashing rain just to get the job done. The tape/adhesive wont stick properly and will probably come off after a very short time undoing all the hard work and making it impossible to put right as a retrofit.
What happens when a roofer trys battening out a roof on a windy day? At the very least they will put several nails through the felt or at worst a foot. The same for pouring concrete in the frost.

Cavity fill insulation is only as good as the blocklayer that built the wall and the insulation installer on the day. My own house was built in 2004 and the contractor at the time used blown in bead insulation. When I looked at it with a thermal camera last year there is no insulation under the window cills and in large patches where I can only assume there were excessive mortar droppings in the cavity or there wasnt enough bead blown in. There is about 500mm of cavity below the wallplate that has no insulation at all. The only thing I can assume is that the beads shrank/settled or the contractor cut corners on the amount used.

It may be an easier solution from the blocklayers point of view but I just dont like the fact that the workmanship cant be seen. There is no way of telling if mortar droppings are bridging the cavity or if voids have been left in the insulation until after the job has been done and at faily hefty expense.

sinnerboy

I respectfully disagree Slig. There is only so much p******g against the wind one can do. The penny dropped with me a long time ago what a farce partial fill construction is and I can see only more problems with full fill boards not less.

In my opinion the only way to do partial fill board is by leaving the outer leaf down , if not entirely , then for decent lifts. And this must not be even attempted with a 100mm inner leaf as it is not stable enough mid build.

Today one should be looking at a 150 min cavity which if kept "free" for blocklaying makes the task of building and inspecting the cavity so much more practical.

Your bad experience of beads sound dreadful but with better supervision can be avoided ( not intended as a dig at you that )

Slig

sinnerboy wrote: »

I respectfully disagree Slig. There is only so much p******g against the wind one can do. The penny dropped with me a long time ago what a farce partial fill construction is and I can see only more problems with full fill boards not less.

In my opinion the only way to do partial fill board is by leaving the outer leaf down , if not entirely , then for decent lifts. And this must not be even attempted with a 100mm inner leaf as it is not stable enough mid build.

Today one should be looking at a 150 min cavity which if kept "free" for blocklaying makes the task of building and inspecting the cavity so much more practical.

Your bad experience of beads sound dreadful but with better supervision can be avoided ( not intended as a dig at you that )

none taken, I wasnt involved in the build of my gaff in any direct manner. Its in an estate that was built in mid boom to typical mid boom housing estate standards. I was a mere cad monkey working with the engineers in charge at the time and as such rarely seen daylight.

I completely agree with your wall build-up except that I would prefer to use a 225/150mm blockwork innerleaf to act as the load bearing structure. This would allow for more freedom when building the outer leaf as it then becomes a rainscreen hanging off the structure.However, In the past I have found it very hard to justify the 50% extra cost in blockwork to the client or the concept of insulation and air tightness to the blocklayer.

sinnerboy

Slig wrote: »

I completely agree with your wall build-up except that I would prefer to use a 225/150mm blockwork innerleaf to act as the load bearing structure.

Absolutely - vital point. Used where 215 inner leaf is otherwise required for structural reasons ( large house and / or concrete upper floors )

just do it

Slig wrote: »

Cavity fill insulation is only as good as the blocklayer that built the wall and the insulation installer on the day. My own house was built in 2004 and the contractor at the time used blown in bead insulation. When I looked at it with a thermal camera last year there is no insulation under the window cills and in large patches where I can only assume there were excessive mortar droppings in the cavity or there wasnt enough bead blown in. There is about 500mm of cavity below the wallplate that has no insulation at all. The only thing I can assume is that the beads shrank/settled or the contractor cut corners on the amount used.

It may be an easier solution from the blocklayers point of view but I just dont like the fact that the workmanship cant be seen. There is no way of telling if mortar droppings are bridging the cavity or if voids have been left in the insulation until after the job has been done and at faily hefty expense.

Unfortunate for you but I'm glad to hear it was an estate house built in the tiger years i.e. understandable that the quality of workmanship was not top drawer, rather than a one-off built and supervised by yourself. Most likely cause is lack of drill holes. In a new build they're plastered over as well so you don't even get to see where they are!


I've visited a poster's self-build who has gone with full fill 220mm cavity. He's done a few things that help keep a clean cavity:

• firstly quality blocklayer
• when the mortar has dried, go around and tap the wall ties and any snots fall to bottom of cavity
• left a block out at either end of bottom of cavity allowing the cavity to be brushed clean - I'd imagine a chimney sweep along the length of the wall a few times would do the trick

Then the bead installer. The house I'm currently living in is a one-off dormer built in 2003 with alot of short cuts. Typical 100mm partial fill cavity. No cavity closers so I was able to have a look down into the cavity. Huge areas had no insulation board at all, particulary around opes. It didn't retain heat it on a cold windy day (its on an exposed site). This winter we took advantage of the grants and insulated the attic and pumped the walls by a guy who came well recommended by some friends of mine in the trade. Attention to detail was excellent. For example under a 2m long window cill he drilled 4 holes 60mm apart, 15mm down from cill. Extra drill holes around wall vents etc. Results are excellent. Heat demand is way down.

I've heard stories of guys who're doing the job and not showing the same level of attention to detail. The big issue as I see it for the average punter is knowing the good guys from the bad. In my experience the good guys aren't usually the best sales men.

sinnerboy

just do it wrote: »

[*]left a block out at either end of bottom of cavity allowing the cavity to be brushed clean - I'd imagine a chimney sweep along the length of the wall a few times would do the trick.

Also leave out 1/2 blocks at c/c 2500mm along wallplate level, at cavity base and to mid cills and heads. Watch the stuff bulge out - tell the installer you want to see this.

Slig

Thats my point, You can see how a board is being fitted at any time during construction and with proper supervision the job will be done right.

IMO its too difficult to inspect the quality and quantity of the insulation with a pumped cavity. If even one of the factors you mentioned is missing, be it the good workmanship of the blocklayer, the removal of the excess mortar from the dpc tray or the attention to detail of the bead installer then the job could be a complete waste of money.

It took me the use of a thermal imaging camera (and 4 years) to get an idea of how badly insulated my own house is (mechanics car syndrome?) and how do you retrofit a repair?

just do it

Slig
Yes, it's a bit s****y that the government has to grant aid improved insulation when if it had been done to good standard to begin with the need wouldn't be as great.

Out of interest, how much did it cost you to get the thermal imagery done?

Slig

just do it wrote: »

Slig
Yes, it's a bit s****y that the government has to grant aid improved insulation when if it had been done to good standard to begin with the need wouldn't be as great.

Out of interest, how much did it cost you to get the thermal imagery done?

Industry discount, a couple of pints and a snag list:D

rural_red

just do it wrote: »

Thanks PUT
Following on from this it's hard to see the justification of a partial fill in the first place. The context here is exposed sites on the western coast line.

So if building in such a location using wide cavity construction (200-250mm), proper placing of wall ties (slanted outwards), clean cavity, use of cavity trays particularly on the SW walls, one should be confident water won't penetrate the inner leaf.

Anyone disagree?

I would not be confident that the inner leaf will remain dry and even if it does there are a few other issues here;

1.
You are ignoring the original purpose of a cavity wall. The external leaf is a rainscreen or sacrificial layer and is expected to get wet. Partial fill insulation maintains the integrity of the cavity. Therefore if you fill the cavity you can expect the insulation in the cavity to get wet.

If you take a close look at wall ties they should have a nook in them that helps to hold insulation back but are actually there to encourage water to drip down into the cavity. Any other type will encourage water to flow over the tie!

http://www.ancon.co.uk/products/wall-ties-and-restraint-fixings/cavity-wall-ties/ties-for-cavities-over-150mm

If the external leaf is wet, then (some of?) the insulation is wet. If insulation is wet its thermal conductivity increases as water is vert conductive. This means that (some of?) the insulation is not performing as designed. Your larger cavity with the fill of more insulation may actually have a peformance equivalent to a partial fill.

Someone mentioned that cavity walls do not have a wet external leaf, however hygrothermal simulation on WUFI says otherwise. Being on a site when it rains also suggests otherwise. Looking at a completed (and rendered) wall that shows discolouration / wet marks following the mortar joints suggests otherwise. Until I see evidence to the contrary I am sceptical with claims that it remains dry.

This is an extract from <mod edit - a full fill bead > IAB cert.-

' Severe Exposure
Severe exposure to wind-driven rain applies in districts where the driving rain index is 5m²/sec/year or more (see Figure 2). During the pre-insulation survey of any particular building, due regard to the exposure zones and type of masonry construction must be assessed prior to the commencement of the installation process.

In severe exposure areas the type of outer leaf masonry finish where <snip> System are suitable is:
Impervious cladding and rendered walls with a minimum cavity width of 90mm and up to 12m in height.

Unrendered brickwork is not suitable for injected full-fill cavity wall insulation in the severe exposure zones.

Weep holes in accordance with good construction practice must be provided at the base of brick faced cavity walls at 450mm centres and over lintels. '

This suggests to me that they expect a wet outer leaf!

2.
There are other more limiting issues with a cavity wall that will probably override any pernickitty discussion about the relative merits of full or partial fill. Take a look below;

http://www.josephlittlearchitects.com/documents/cavity_wall_paper.pdf

He concludes that partial-fill cavities suffer from degradation of thermal peformance due to thermal looping while full-fill suffers a degradation of performance due to moisture.

3.
It is becoming clear to me that the 'traditional' method of cavity wall is becoming defunct. I have used both partial and full fill in the past but as suggested early in this thread, another solution may be best?

sinnerboy

rural_red wrote: »

In severe exposure areas the type of outer leaf masonry finish where <snip - bead fill> are suitable is:
Impervious cladding and rendered walls with a minimum cavity width of 90mm and up to 12m in height.

That's how I read it rural red.

So

If new build - must be 150mm cavity min (imo)
If in severe exposure area - you gotta render.

rural_red

sinnerboy wrote: »

That's how I read it rural red.

So

If new build - must be 150mm cavity min (imo)
If in severe exposure area - you gotta render.

I don't dispute your reading of where they say it is suitable. if you reread my highlights (in bold) I am underlining their understanding and assertion that the outer leaf will likely be wet. They make great pains to remediate against this wettness...be that an impervious rainscreen, a weather proofing render or weepholes to allow water flow back out from cavity. The reality is that in blockwork with a sand and cement render you can expect the outer leaf to be wet (sand and cement is not waterproof, hence the watermarks on walls highlighting the tracks of mortar joints!!) - even this manufacturer expects it thus. That is my point. For further proof compare their specification for less exposed parts of the country.

I once had a blocklayer try and convince me that sand and cement render would prevent water from entering a chimney stack and that I did not need a lead tray...a wet week later he was installing the tray

sinnerboy

We agree.

The outer leaf is gauranteed to get wet. Very wet. Water will flow down the inner face of the outer leaf no question. And full fill will be devalued accordingly.

To what extent I can't honestly say but my judgement would lead me to expect that no more than the first 25mm "layer" would be affected that's all. I would like of course to see some research paper on the subject to confirm this. Or indeed a WUFI calc. ( Can't use it - yet )

Be careful about reading too much into the article you linked to on this point. The author is relying in part on BRE research conducted circa 1999 which compared calculated U Values with measured on site real U Values and that report highlighted widescale bad workmanship for every build type. ( surprise surprise :rolleyes:)

rural_red

sinnerboy wrote: »

We agree.
Be careful about reading too much into the article you linked to on this point. The author is relying in part on BRE research conducted circa 1999 which compared calculated U Values with measured on site real U Values and that report highlighted widescale bad workmanship for every build type. ( surprise surprise :rolleyes:)

My reading of his article is that the BRE report established that timberframe performed remarkably well !! He has a distribution diagram explaining this.

Since we have no research that I know of on the flow of water from external leaf across bonded bead or full-fill insulation of any type then we should be cautious. Until then we are working on subjective intuition / guesswork which is not the best place to begin when building a construction method that we have no access to after completion.

sinnerboy

We have the IAB certs in the meantime.

You should seek out the BRE report yourself and read it.

rural_red

sinnerboy wrote: »

We have the IAB certs in the meantime.

You should seek out the BRE report yourself and read it.

I am dissappointed with your response afterall there are IAB certs for both partial fill boards and bonded bead. So this reliance on IAB certs does not progress the discussion.

The author of that report kindly extracted the dustribution graph from the BRE report...are you saying that his diagram is not from the report?

galwaytt

sinnerboy wrote: »

The outer leaf is gauranteed to get wet. Very wet. Water will flow down the inner face of the outer leaf no question. And full fill will be devalued accordingly.

To what extent I can't honestly say but my judgement would lead me to expect that no more than the first 25mm "layer" would be affected that's all. I would like of course to see some research paper on the subject to confirm this. Or indeed a WUFI calc. ( Can't use it - yet )

Well, I've been down this road personally, and my comprehension of the situation is that the outer face, of the outer leaf will always get wet. No issue there. Then, it dries from the top (gravity, wind, airflow). And, just as in roofing, you can get the effect where all the water that flows from all of the wall surface........will tend to keep the bottom wet, more or less all the time. Or at least moist, a lot of the time. But the wall will always be drying, or trying to. Gravity and airflow see to that.

Now, in section across the wall, the damp will not penetrate to the extent of running down the inside surface of the outer leaf, except in cases of actual rainscreen penetration (say, a crack, leaking expansion joint, poor DPC at a cill or something etc.), where the ability to absorb the damp, through capillary action, within the material itself may be overcome (saturation). This is unlikely at the tops of walls, but more likely towards the bottom. You still have the effect's of gravity and air flow generally tending to dry out the inner face, within the cavity. Pumped cavity insulation should, if you follow logic, allow anything that is there, to flow, by capillary and gravity, downwards - not horizontal. The wider the cavity the 'safer' you are, and moisture should always head in one direction........downwards.

Which is why we should have a step in the foundation/DPC at floor level. This way, any measures or material which may be overcome......will still follow the rules of gravity, and drain away at bottom of cavity.

As for boards instead of pump fill, well, the only path across is the ties. And ties have drip features - naturally if you're using a full-fill board, that drip feature needs to be outside of the boardface, otherwise you will actually encourage water into the board. Long term, bad for the board (if not PS based). Has anyone seen such a tie ?

But a lot of this is exceptional case stuff, and the key to a lot of it is good workmanship so that it can't come up in the first place.

Sorry, gibbering, at this late hour.............

just do it

sinnerboy wrote: »

That's how I read it rural red.

So

If new build - must be 150mm cavity min (imo)
If in severe exposure area - you gotta render.

What then is a suitable render?

RKQ

just do it wrote: »

• firstly quality blocklayer
• when the mortar has dried, go around and tap the wall ties and any snots fall to bottom of cavity
• left a block out at either end of bottom of cavity allowing the cavity to be brushed clean - I'd imagine a chimney sweep along the length of the wall a few times would do the trick

Great advice. Leaving a block out at either end of bottom of cavity is very clever. So easy to clean out the cavity.:)

sydthebeat

RKQ wrote: »

just do it wrote: »

• firstly quality blocklayer
• when the mortar has dried, go around and tap the wall ties and any snots fall to bottom of cavity
• left a block out at either end of bottom of cavity allowing the cavity to be brushed clean - I'd imagine a chimney sweep along the length of the wall a few times would do the trick

Great advice. Leaving a block out at either end of bottom of cavity is very clever. So easy to clean out the cavity.:)

I'm not so sure pushing hard set concrete along a plastic dpc layer is such a great idea, although I applaud the initive.

RKQ

sydthebeat wrote: »

I'm not so sure pushing hard set concrete along a plastic dpc layer is such a great idea, although I applaud the initive.

Fair point if you are not using a reinforced radon barrier.

Then again, cement snots are quite light weight and if you are going to these lengths to brush the snots out, then it would be worth installing 18inch pvc damp course as protection to the dpm / radon barrier during brushing. A 2nd layer of dpm plastic or reinforced radon barrier could be used as alternatives.

Poor Uncle Tom

RKQ wrote: »

A 2nd layer of dpm plastic or reinforced radon barrier could be used as alternatives.

It's hard enough to get them to put one in....:D

Actually, a layer of sand in first would make it much easier to clear out in the end.

sinnerboy

just do it wrote: »

What then is a suitable render?

The outer leaf of a cavity wall protects the internal leaf from moisture penetration by 3 mechanisms.

1. Flow off from the outer surface of the wall
2. Absorbtion and desorbtion via the fabric of the outer leaf ( wetting and drying
3. Drain down along the inner face of the outer leaf which must be collected and forced outwards by stepped dpcs located over openings and at the cavity base.

Any render will contribute to the first mechanism.

Smooth renders , to my eye anyway , look best. However in high exposure areas ( the entire coast line and anywhere west of the Shannon ) water can run in film down such walls. If there are any defects ( cracks ) thin water is in like Flynn. Therefore textured renders work better. A pebble dashed of eben dry dashed render using aggregates on 15mm + will prevent water form forming a continuous film of run off .