Cavity wall Insulation ideas

john f 4g63

Hi all,
I have been looking on this website with quiet awhile but this is my first time posting.
Have to say i find it very informative in a lot of areas.

I hope to be starting a new build at start of next year so would just like to ask a few questions regarding insulation. Just wish there was a right and a wrong type of insulation as so many types now.

Im thinking of just putting all the insulation in the cavity but don't want to have a 250-300 mm cavity either. I'm guessing the best way then is to go partial fill, as in order to get a good insulation value with beads then i would need a very wide cavity. I am thinking of using a cavity width of approx 150mm. Here are the options i was thinking :

1) Use 140mm pir insulation

2) Use an 80mm and a 60mm pir insulation and stagger the joint.

3) Use 80mm pir insulation and pump the rest of the cavity.

I would appreciate any suggestion on the above as with so many on here my head is wrecked from trying to choose the best insulation.

Thanks in advance

fealeranger

A BER is your way to go. That cavity wall spec will be tricky.

john f 4g63

Ya, The reason i am thinking option 2 and 3 is the main problem with the pir insulation is getting the blocklayers to fit it correctly. i was hoping this way by either putting 2 layers and staggering the insulation or by putting one layer and pumping the rest that would help to make sure insulation gets everywhere.

Has anyone ever done it these ways or is it a bad idea full stop?

fealeranger

Like I said, get the BER guy. This is his thing. He will design for you, if it can be done he will do it.

BryanF

John, start with construction details, beed full fill is the quickest and easiest option.

BryanF

fealeranger wrote: »

Like I said, get the BER guy. This is his thing. He will design for you, if it can be done he will do it.

I think this should come with a caveat that the 'BER assessor' must have a background qualification in arch or eng to offer the service you suggest

john f 4g63

BryanF wrote: »

John, start with construction details, beed full fill is the quickest and easiest option.

Ya i have taught of just going with the beads as it ticks a lot of boxes only i don't think 150mm pumped is enough of insulation? If i was doing it this way id probably have to put the insulated slab on inside as well. The only reason i don't want to do this then is i'm thinking of using an air to water heat pump and underfloor heating so don't want to lose out on the thermal store from the inside wall.

Rock12

Have you thiught of using a 200mm cavity using certified fibre glass wall ties. Fully pumped with platinum bead insulation. This should give you a good U value in one layer of insulation leaving you the use of the inner wall as a thermal store.
With attention to detail at the openings and rising walls,etc it would be another option.

john f 4g63

Rock12 wrote: »

Have you thiught of using a 200mm cavity using certified fibre glass wall ties. Fully pumped with platinum bead insulation. This should give you a good U value in one layer of insulation leaving you the use of the inner wall as a thermal store.
With attention to detail at the openings and rising walls,etc it would be another option.

Yes that is another option I was considering but I was thinking if I used pir insulation instead of beads then could i achieve the same uvalue but with a smaller cavity?

Cavanjack

I asked the same question here a few months ago. I was thinking of going with a 200mm pumped cavity. I have since decided to go 250mm full fill. I am also going with some form of geothermal wether it be air to water or ground sourced and for this reason I decided against internal insulation. Although nearly every builder I have spoken to has told me I'm mad not to "stick the cozy board inside the external walls".

archtech

Cavanjack wrote: »

I decided against internal insulation. Although nearly every builder I have spoken to has told me I'm mad not to "stick the cozy board inside the external walls".

2 years ago I would have told you the same that you but in terms of cost alone i would rule it out now. Putting all your insulation together in one zone is much better and generally reduces the risk of interstitial condensation occurring where you don't want it to occur.

As for the best solution a wide cavity with bead is fairly robust once one overcomes the detailing around opes, at eaves level etc A PIR board type insulation reduces the required width of the cavity but requires great care from the block layers. Another option is external insulation many are nervous that it is not robust enough and will be damaged by junior playing ball.... To be honest how many kids theses day are left play ball against a wall of a house anyway.

The best advise is keep all your insulation together, and don't mix and match types within the same wall.

john f 4g63

Cavanjack wrote: »

I asked the same question here a few months ago. I was thinking of going with a 200mm pumped cavity. I have since decided to go 250mm full fill. I am also going with some form of geothermal wether it be air to water or ground sourced and for this reason I decided against internal insulation. Although nearly every builder I have spoken to has told me I'm mad not to "stick the cozy board inside the external walls".

If i was thinking of using oil and rads as my heating then i probably would consider the insulated slab on the inside so as every time i turned on the heating the wall wouldn't soak up the heat but with underfloor i just think it makes since not using the insulation slab inside. I reckon its just become the norm for most builders to use it but if not fitted correctly again then it isn't as effective and costly. So i think i will just keep all the insulation to inside the cavity where it cant be damaged or interfered with. Just picking which one now is the problem?
Does anyone else have any feedback as to the ideas i suggested at the start of this thread?

yop

Cavanjack wrote: »

I asked the same question here a few months ago. I was thinking of going with a 200mm pumped cavity. I have since decided to go 250mm full fill. I am also going with some form of geothermal wether it be air to water or ground sourced and for this reason I decided against internal insulation. Although nearly every builder I have spoken to has told me I'm mad not to "stick the cozy board inside the external walls".

Would go with the insulated slabs myself after finding them very good in the new officespace I built above the shed.
Aerothermal I wouldn't recommend to be honest, have heard more bad than good stories about it and its the lowest COP of all of them. Have geothermal ourselves with the sand bed, but borehole seems to be the best option.
I would actually avoid them altogether and pump the money into insulation and a blow test. Something like a condenser boiler then with small rads in a highly insulated house should work out well.

rockabaloo

I would go for a well finished fully pumped 150mm cavity if you're keen on a smaller cavity. The extra 50mm or 100mm doesn't make that much difference. I think time and money are better spent making sure the house is as airtight as possible. Heat loss through ventilation makes a massive difference to indoor temperatures.

archtech

rockabaloo wrote: »

I would go for a well finished fully pumped 150mm cavity if you're keen on a smaller cavity. The extra 50mm or 100mm doesn't make that much difference. I think time and money are better spent making sure the house is as airtight as possible. Heat loss through ventilation makes a massive difference to indoor temperatures.

At a cavity of only 150mm you are right at the maximum permitted u-value of 0.21w/m2k for any of the platinum pumped beads and will be very much dependant on other factors (often more expensive) to achieve compliance with Part L . Beefing up the cavity by 50mm with reduce your u-value to around 0.17w/m2k or better depending on the wall ties used which is a good improvement. Please note that the exact u-value is dependant on a calculation based on the exact wall build up.

john f 4g63

archtech wrote: »

At a cavity of only 150mm you are right at the maximum permitted u-value of 0.21w/m2k for any of the platinum pumped beads and will be very much dependant on other factors (often more expensive) to achieve compliance with Part L . Beefing up the cavity by 50mm with reduce your u-value to around 0.17w/m2k or better depending on the wall ties used which is a good improvement. Please note that the exact u-value is dependant on a calculation based on the exact wall build up.

That is what i was thinking as i don't want to be on the limit with a u-value of 0.21. That's why i was thinking putting 80mm pir insulation and pumping the rest to make up 150mm as wouldn't this bring my u-value under the regulation of 0.21?
You said earlier in a post not to mix and match the insulation. Is it just as it is too messy or is there other reasons?

rockabaloo

What about a 175mm pumped full filled cavity then? Will meet the regs with no problems, is not much thicker and is easiest to build.

heavydawson

rockabaloo wrote: »

What about a 175mm pumped full filled cavity then? Will meet the regs with no problems, is not much thicker and is easiest to build.

Our new build has a 150mm cavity with 150mm Xtratherm Cavitytherm insulation. On-paper U-value of 0.12. Stress the "on-paper".
Our blocklayer is excellent though, and we're using all of the appropriate corner, riser, and top sections available to ensure the job is neat.

We're a long way from being in the house, but for someone like yourself with a 150mm cavity, I thought it was worth a mention.

archtech

john f 4g63 wrote: »

That is what i was thinking as i don't want to be on the limit with a u-value of 0.21. That's why i was thinking putting 80mm pir insulation and pumping the rest to make up 150mm as wouldn't this bring my u-value under the regulation of 0.21?
You said earlier in a post not to mix and match the insulation. Is it just as it is too messy or is there other reasons?

First of all you have two completely different materials which react differently , which is not a great start, also from a construction point of view you will end up with a narrow cavity which will be hard to keep clean and free from mortar dropping, prior to pumping it. Pumped bead suits wide cavities that can be easily kept clean and inspected. It is used in existing wall upgrades for convenience and because its relatively cheap.

john f 4g63

heavydawson wrote: »

Our new build has a 150mm cavity with 150mm Xtratherm Cavitytherm insulation. On-paper U-value of 0.12. Stress the "on-paper".
Our blocklayer is excellent though, and we're using all of the appropriate corner, riser, and top sections available to ensure the job is neat.

We're a long way from being in the house, but for someone like yourself with a 150mm cavity, I thought it was worth a mention.

Is that the fullfill cavity insulation? Been looking into that as well as is another option if i only want 150mm cavity. Find it odd how this insulation can fit up against the outside leaf where as you need to leave at least 40mm gap for the other type of insulation, When they look the same.
What does your blocklayer think of it fitting wise?

heavydawson

john f 4g63 wrote: »

Is that the fullfill cavity insulation? Been looking into that as well as is another option if i only want 150mm cavity. Find it odd how this insulation can fit up against the outside leaf where as you need to leave at least 40mm gap for the other type of insulation, When they look the same.
What does your blocklayer think of it fitting wise?

Hey John,
Yup, full fill. There's a HIP (High Impact Polystyrene) facing of 30mm on the outside of the board with built-in flutes of 5mm that serve to maintain a 5mm air gap between the outside of the board and the outer leaf and also act as mini-cavity trays (on paper). You can see all of the details in the BBA cert on the CavityTherm site.
Here's the gotchas:
1. Your blockwork needs to be very clean (no snots, etc). This is a given for any type of insulation
2. You should use the proper corner/riser/top panels that Cavitytherm provides.
3. Boards should be sitting good and tight against the inner leaf to prevent thermal looping.

Blocklayer has fitted the boards in two other houses and doesn't have any problems with it. To be fair though, any blocklayer worth his salt shouldn't moan about the type of insulation being used.
It's certainly slower that building the walls first and pumping after, and I'm taking a chance of sorts as the product is relatively new to market, but I was looking for an on-paper whole house insulation envelope of 0.12, and this fit my needs. I've attached a few photos to show you the insulation on site

just do it

rockabaloo wrote: »

What about a 175mm pumped full filled cavity then? Will meet the regs with no problems, is not much thicker and is easiest to build.

I thought 150mm is the limit before extra wall ties are required. Therefore if going greater than 150mm, you may as well go to 200, 220 or 250mm.


Ultimately I think putting the house through PHPP is the way to go. Then it is easier to see the effect of the different wall build-ups, not to mention the effect of all the other elements of the build on the houses heat demand.

blast06

'Heavydawson' ..... just curious re your photos - why is there a layer of DPC (the black stuff!) between the external wall and the cavitytherm insulation and why only close to the windows. I'm somewhat of a novice so perhaps an obvious answer ?

Also, John - have you considered Quinn lite blocks on the inner leaf ? I am building an have a 6" pumped platinum bead cavity with B5 quinn lite blocks on the inside leaf achieving a u-value of 0.16

heavydawson

blast06 wrote: »

'Heavydawson' ..... just curious re your photos - why is there a layer of DPC (the black stuff!) between the external wall and the cavitytherm insulation and why only close to the windows. I'm somewhat of a novice so perhaps an obvious answer ?

Also, John - have you considered Quinn lite blocks on the inner leaf ? I am building an have a 6" pumped platinum bead cavity with B5 quinn lite blocks on the inside leaf achieving a u-value of 0.16

Blast, good question! I did a little digging and I think this thread explains a lot:
http://www.boards.ie/vbulletin/showthread.php?t=2056075250

john f 4g63

blast06 wrote: »

'

Also, John - have you considered Quinn lite blocks on the inner leaf ? I am building an have a 6" pumped platinum bead cavity with B5 quinn lite blocks on the inside leaf achieving a u-value of 0.16

No hadn't considered doing this. Would it not end up a lot dearer as aren't the quinn lite blocks a lot more expensive then standard blocks?

heavydawson

john f 4g63 wrote: »

No hadn't considered doing this. Would it not end up a lot dearer as aren't the quinn lite blocks a lot more expensive then standard blocks?

They're more expensive, and you'll also need to factor in that they only deliver to certain parts of the country once a week, so you'll need to order with plenty of notice. I'm building in Tipperary, and one of our orders was delayed a week because the protests that took place outside the factory gates relating the Quinn family situation. Very little the company could do to be fair, but the one week delay can be a bit of a pain

blast06

Re the Quinn lite blocks .... i ordered a lorry load about 3 weeks ago and had the blocks the following evening - about 80 mile delivery. If i run short, then local building supplier always has 500 or so in stock to cover punters like me who might run short.
They retail at ~€1 per block compared to 40-45c per concrete block so in my case about €1200 spent .... however, this is more or less the same cost as putting in a 2" insulated slab when extra labour cost is considered .... and based on what reading i have done, i would go with the Quinn lite block over the insulated slab 7 days a week.


heavydawson .... sure enough i have to have the extra DPC later as well. I built another house about 7 years ago and don't recall having to use it.

build120

Hi,I am building a cavity (150mm) i will shortly be starting on the block work for my house.the insulation i am looking at is either of the these threeXtratherm 140mm board, Kingspan 140mm board or a Kingspan aerobord platinum 140mm board.each are classed as full 150mm insulation as they have the plastic on outside(10mm) to allow moisture to run off. has anyone used any of these and if you have how did you find the performance.

thanks

Build120

just do it

build120 wrote: »

Hi,I am building a cavity (150mm) i will shortly be starting on the block work for my house.the insulation i am looking at is either of the these threeXtratherm 140mm board, Kingspan 140mm board or a Kingspan aerobord platinum 140mm board.each are classed as full 150mm insulation as they have the plastic on outside(10mm) to allow moisture to run off. has anyone used any of these and if you have how did you find the performance.

thanks

Build120

why not pump the cavity?

build120

Hi just do it,

yeah not a big fan.once you pump no going back. i have heard of a few houses new builds with moisture problems. I know costs involved so far are cheaper for the pumped. but i would still like the full fill board.

BryanF

build120 wrote: »

Hi just do it,

yeah not a big fan.once you pump no going back. i have heard of a few houses new builds with moisture problems. I know costs involved so far are cheaper for the pumped. but i would still like the full fill board.

So the eps type you mention will have low thermal resistance than the PIR types.
As regards moisture problems I question if this has anything to do with the Insultion, more likely a mixture of thermal bridging and lack of appropriate ventilation. The full fill boards are slower to fit and their continuity is down to the block layer who traditionally have not paid much attention to insulation.

build120

Hi Bryan F,

no the eps is at ? i will have to ask the supplier and the pir 6.9 resistance
for the Xtratherm. yes i agree about the boards and block layer but i have already discussed this with them. i gather your not a fan of the eps.

BryanF

build120 wrote: »

Hi Bryan F,
i gather your not a fan of the eps.

Not true at all! EPS is cheaper! But you need More of it for the equivalent width of PIR.

build120

Would the additional performance of a pir vs eps justify 45% extra in price.

i have been told by suppliers that 150mm fullfill bead would be comparible to 80mm pir.

this is also a reason why i am looking more so at the full fill board than full fill cavity.

thanks for your quick replys