Wall Construction / Insulation Question

Cork selfbuild

Hi there,

We are in the process of trying to finalise our tender for our house and after reading a few posts / articles about the wider the cavity etc is better and avoid the internal insulation due to questions about dampness inside the board, rooms cool down quicker etc, the original proposal from him was on the RHS and I asked about the LHS option...



He said that the 250mm Cavity was not advised as it would compromise the structure, I'm not in the know hear hence the post.

We have a full concrete slabbed first floor and concrete stairs, house is a 2 story and covers 2700 sq ft, and has a large open plan kitchen / living / dining space with about 30ft+ of glazing here in this room (sorry don't know if this makes a difference)

I also asked about the BER, and he says should be B1, now again not that knowledgeable as to what the norm non passive is here, we did say we wanted it to be really well insulated, low energy demand.

The heating is Air to Water with a Stove x 2 and no open fire, triple glazed "PassIV Window U-value as low as 0.5W/m²K (Centre pane U-value of 0.299W/m²K)" standard windows.

So what I'm asking is what would be the advised route re wall's / insulation because we don't want to get it wrong and I am happy to spend a bit more at the start to get it right... Any advice or help much appreciated.

hexosan

Who told you the 250mm cavity would compromise the structure as that's total BS. Numerous people are building using 250mm wide cavity (myself included).

Why are you considering block on the flat for the internal leaf. I went with 100mm block on the edge and I've two floors of concrete slabs.

If your engineer is saying you need the block on the flat internal leaf then I suggest you go with external insulation because the money you spend on the cavity insulation and extra labour and materials building the external leaf will off set the cost of the external insulation.

BryanF

Cork selfbuild wrote: »

Hi there,

We are in the process of trying to finalise our tender for our house and after reading a few posts / articles about the wider the cavity etc is better and avoid the internal insulation due to questions about dampness inside the board, rooms cool down quicker etc, the original proposal from him was on the RHS and I asked about the LHS option...



He said that the 250mm Cavity was not advised as it would compromise the structure, I'm not in the know hear hence the post.

We have a full concrete slabbed first floor and concrete stairs, house is a 2 story and covers 2700 sq ft, and has a large open plan kitchen / living / dining space with about 30ft+ of glazing here in this room (sorry don't know if this makes a difference)

I also asked about the BER, and he says should be B1, now again not that knowledgeable as to what the norm non passive is here, we did say we wanted it to be really well insulated, low energy demand.

The heating is Air to Water with a Stove x 2 and no open fire, triple glazed "PassIV Window U-value as low as 0.5W/m²K (Centre pane U-value of 0.299W/m²K)" standard windows.

So what I'm asking is what would be the advised route re wall's / insulation because we don't want to get it wrong and I am happy to spend a bit more at the start to get it right... Any advice or help much appreciated.

I recommend you keep the insulation in the one place, you should push for a provisional BER before planning. I strongly recommend this glazing company is given very detailed drawings at tender stage and that shop drawings are demanded. At this stage, With that amount of glazing your architect had better be looking at some form of external shading. And also at tender stage, considering thermal bridging and generally the buildings air-tightness.

Regarding compromising the wall structure... There is a solution to this but it specific to your house and your structural engineer should advise.

What evidence has been provided that the heat pump will efficiently offer you hot water & heat the house?

Cork selfbuild

hexosan wrote: »

Who told you the 250mm cavity would compromise the structure as that's total BS. Numerous people are building using 250mm wide cavity (myself included).

Why are you considering block on the flat for the internal leaf. I went with 100mm block on the edge and I've two floors of concrete slabs.

If your engineer is saying you need the block on the flat internal leaf then I suggest you go with external insulation because the money you spend on the cavity insulation and extra labour and materials building the external leaf will off set the cost of the external insulation.

This was the response from the engineer, it was short and over email to which I'm going to bring up in our meeting in a few days.

Also I've heard mixed reviews over the external insulation, the cost and only offering 30 yr guarantee etc, i'd prefer not to have this as an option.

BryanF wrote: »

I recommend you keep the insulation in the one place, you should push for a provisional BER before planning. I strongly recommend this glazing company is given very detailed drawings at tender stage and that shop drawings are demanded. At this stage, With that amount of glazing your architect had better be looking at some form of external shading. And also at tender stage, considering thermal bridging and generally the buildings air-tightness.

Regarding compromising the wall structure... There is a solution to this but it specific to your house and your structural engineer should advise.

What evidence has been provided that the heat pump will efficiently offer you hot water & heat the house?

Yes I should have gotten the provisional BER done before now, but we have already been granted planning in January this year... Yes we are in discussion with 3 glazing companies already, we actually engaged in this before planning to discuss and go through, and yes Architect has put in provision for a Pagoda and is spec'd in the tender.

On the wall cavity / insulation this is one of the main points we will be discussing in the meeting in a few days, I suppose I just wanted to try understand it slightly better myself in the interim... I'd prefer block on the inside and outside but want to ensure the insulation & cavity are sufficient for a comfortable home. Will look into the Thermal Bridging and Air Tightness over the w/e...

There will also be solar for DHW, and looking into the backup of a stove w/bb to see if possible to loop into the DWH system, looking at a few external companies myself for the heating demand and meeting it. Not too sold on the A2W yet and it may be removed for a different system, here what worries me is if its up to the job and how costly will it be to run...

HoofRocks

Did you consider xtra therm cavity therm 150 ml board insulation. Will meet current regs and keep your insulation all in one place. Also smaller cavity.

Could be an option.

Cork selfbuild

Is this not what the engineer was suggesting excluding the 62.5mm internal insulation as per the image on the LHS in the OP? Sorry if not!

BarneyMc

I have a 250mm cavity and my engineer specified a 6 inch (150mm) block on the inner leaf on the ground floor. ** This will depend greatly on the dimensions, layout, etc. of your house so checking what others did is not going to help. It is up to your engineer to sign off on this and therefore what they're happy with. **

Make sure to provide external air supplies for your 2 stoves.

gooseygander

Cork selfbuild wrote: »

Hi there,

We are in the process of trying to finalise our tender for our house and after reading a few posts / articles about the wider the cavity etc is better and avoid the internal insulation due to questions about dampness inside the board, rooms cool down quicker etc, the original proposal from him was on the RHS and I asked about the LHS option...



He said that the 250mm Cavity was not advised as it would compromise the structure, I'm not in the know hear hence the post.

We have a full concrete slabbed first floor and concrete stairs, house is a 2 story and covers 2700 sq ft, and has a large open plan kitchen / living / dining space with about 30ft+ of glazing here in this room (sorry don't know if this makes a difference)

I also asked about the BER, and he says should be B1, now again not that knowledgeable as to what the norm non passive is here, we did say we wanted it to be really well insulated, low energy demand.

The heating is Air to Water with a Stove x 2 and no open fire, triple glazed "PassIV Window U-value as low as 0.5W/m²K (Centre pane U-value of 0.299W/m²K)" standard windows.

So what I'm asking is what would be the advised route re wall's / insulation because we don't want to get it wrong and I am happy to spend a bit more at the start to get it right... Any advice or help much appreciated.

Hi Cork Self Build, we have a very similar type build to yours (same size, heating, stoves, triple glaze etc.)and received spec from the arc today. It is suggested 100mm concrete block to exter wall, 140mm cavity with 120mm rigid insulation, internal 100mm concrete block with 62.5 warmboard on internal walls. We just got the e-mail today and I don't really know to what standard this spec is except it looks similar to yours, any comments/advice from yourself as we have not massive knowledge on what is poor,good,or very good type of insulation.

MicktheMan

The days of just looking at, for instance, the insulation and u-value of the walls in isolation are long gone (or, at least, should be) and you really should be considering the insulation, ventilation, thermal bridging, air tightness, thermal mass, heating method, heating control and then some as a whole and how these different elements will work together to deliver a comfortable, healthy and affordable home. Too often, different (and often non-compatible) elements are stitched together resulting in an expensive disappointment.

An example of this is where internal insulation in addition to cavity insulation in a new build is spec'ed. This is nonsense and is generally chosen by un-informed/lazy specifiers solely in order to comply with part L.

gooseygander

MicktheMan wrote: »

The days of just looking at, for instance, the insulation and u-value of the walls in isolation are long gone (or, at least, should be) and you really should be considering the insulation, ventilation, thermal bridging, air tightness, thermal mass, heating method, heating control and then some as a whole and how these different elements will work together to deliver a comfortable, healthy and affordable home. Too often, different (and often non-compatible) elements are stitched together resulting in an expensive disappointment.

An example of this is where internal insulation in addition to cavity insulation in a new build is spec'ed. This is nonsense and is generally chosen by un-informed/lazy specifiers solely in order to comply with part L.

Thanks Mick, but if cork self build and my insulation specs are lazy and nonsense, have you any suggestions as to what they should be?, thanks in advance.

hexosan

MicktheMan wrote: »

This is nonsense and is generally chosen by un-informed/lazy specifiers solely in order to comply with part L.

+1 on this
Typical example of a copy & paste job by architect or engineer who is too lazy to educate themselves

gooseygander

hexosan wrote: »

+1 on this
Typical example of a copy & paste job by architect or engineer who is too lazy to educate themselves

Thanks Hex, but any suggestions what it should be as opposed to what it should not be, thanks in advance

MicktheMan

gooseygander wrote: »

Thanks Mick, but if cork self build and my insulation specs are lazy and nonsense, have you any suggestions as to what they should be?, thanks in advance.

They should be such that the finished product is more or less guaranteed to be what you want in terms of comfort, health, affordability.

Can your specifier guarantee the above?

Where I'm coming from is I am generally called in to test (new) houses which are cold, cost a fortune to heat and/or have mould problems. When I finish my testing and demonstrate what the problems are and why it is now quite difficult to remedy, I am invariably asked "why didn't we speak to someone like you before we built?"

So some questions for your specifier:
Do they understand thermal bridging and its importance?
Have they experience with transient hygrothermal behaviour modelling?
Do they understand air tightness / have the experienced an air tightness test. What was the result on their last project. What/why is their target for your project, and how will it be achieved. What ventilation, heating distribution & control and why? Pro's/con's of these etc etc

gooseygander

MicktheMan wrote: »

They should be such that the finished product is more or less guaranteed to be what you want in terms of comfort, health, affordability.

Can your specifier guarantee the above?

Where I'm coming from is I am generally called in to test (new) houses which are cold, cost a fortune to heat and/or have mould problems. When I finish my testing and demonstrate what the problems are and why it is now quite difficult to remedy, I am invariably asked "why didn't we speak to someone like you before we built?"

So some questions for your specifier:
Do they understand thermal bridging and its importance?
Have they experience with transient hygrothermal behaviour modelling?
Do they understand air tightness / have the experienced an air tightness test. What was the result on their last project. What/why is their target for your project, and how will it be achieved. What ventilation, heating distribution & control and why? Pro's/con's of these etc etc

Thanks Mick, I will bring it up with arc after the weekend. Not a sod has been turned on our build yet and really want to try get it right from the off, not great to hear insulation spec is so wrong

hexosan

gooseygander wrote: »

Thanks Mick, but if cork self build and my insulation specs are lazy and nonsense, have you any suggestions as to what they should be?, thanks in advance.

External insulation if you engineer is adamant that you need to use block on the flat internal leaf, plus makes the thermal bridge detailing a lot easier.

If not that then go with a 250mm pumped wide cavity.

BarryM3

A 120mm cavity with pumped insulation and 62mm insulated board is what my structural engineer has recommended too!

Very disturbing to hear this being called lazy and nonsense but I would absolutely prefer to find out now, so thanks!

Is this spec not recommended based on actual hard facts/info or is it just matters of opinion? If it's the former could anyone point me towards some independent tests that support the short comings of this method..... I would then present to the engineer and see what he has to say.

A layman asking the questions Mick has outlined would be a little futile IMO as the layman probably in most cases doesn't understand enough to counteract what could be bluff answers with any degree of fortitude.

I'm always one to seek professional advice but it appears in this case that some professionals are more professional than others!

<snip, read forum charter>

Supersonic42

The inner leaf of an external wall takes the load of the building therefore the size of the cavity should be irrelevant. The outer leaf effectively just protects the inner leaf from the elements so I cannot see any reason why it needs to be a block on the flat, unless the load is very heavy. Also having no insulated plasterboard on the inside allows the inner leaf to absorb heat and keep your house warmer for longer.

Rabbo

Supersonic42 wrote: »

The inner leaf of an external wall takes the load of the building therefore the size of the cavity should be irrelevant. The outer leaf effectively just protects the inner leaf from the elements so I cannot see any reason why it needs to be a block on the flat, unless the load is very heavy. Also having no insulated plasterboard on the inside allows the inner leaf to absorb heat and keep your house warmer for longer.

The size of the cavity isn't totally irrelevant when it comes to structure. The two leafs are structurally tied to each other with wall ties. When you increase the cavity , you reduce the effectiveness of the wall ties therefore requiring more. If you were to build a two storey house in single leaf 100mm block, it probably wouldn't last long

bryaj

how disappointing that some architects & engineers unable to specify what is required are now to police building regulations -

BryanF

BarryM3 wrote: »

A 120mm cavity with pumped insulation and 62mm insulated board is what my structural engineer has recommended

?

what is u-value of the 120 bead wall? And What is the internal surface temp of the inner block face, at locations where internal walls meet the external wall and insulated plasterboard continuity is broken.

archtech

BarryM3 wrote: »

A 120mm cavity with pumped insulation and 62mm insulated board is what my structural engineer has recommended too!

Very disturbing to hear this being called lazy and nonsense but I would absolutely prefer to find out now, so thanks!

Is this spec not recommended based on actual hard facts/info or is it just matters of opinion? If it's the former could anyone point me towards some independent tests that support the short comings of this method..... I would then present to the engineer and see what he has to say.

A layman asking the questions Mick has outlined would be a little futile IMO as the layman probably in most cases doesn't understand enough to counteract what could be bluff answers with any degree of fortitude.

I'm always one to seek professional advice but it appears in this case that some professionals are more professional than others!

<snip>

Ask your consultant to provide results of the condensation risk analysis of his proposed construction. Based on my experience and analysis of similar type construction I would not be happy with a client going down that construction method, nor would I recommend it.

Within the last 4-5 years The energy element of the building regulations (Part L) has become very specialised, with building science having an impact and not all professionals within the industry are upto speed. Most of those with a good knowledge and understanding have done some form of additional training.(and not just a BER course)

There's a number of regular contributors whom for the last number of years have provided solid advice based on detailed analysis and experience.

BryanF

[So some questions for your specifier:
Do they understand thermal bridging and its importance?
c

Where is the air-tightness line going to be in the wall construction

vertico

BryanF wrote: »

what is u-value of the 120 bead wall? And What is the internal surface temp of the inner block face, at locations where internal walls meet the external wall and insulated plasterboard continuity is broken.

Why would internal walls meet external

archtech

bryaj wrote: »

how disappointing that some architects & engineers unable to specify what is required are now to police building regulations -

And some of those whom are best positioned to do so, have been excluded.

BryanF

vertico wrote: »

Why would internal walls meet external

Sorry to be clearer. Where The partition internal walls meet the inner face if the external walls. Ie where very the drylining isn't

Bubbling

What about using a 100mm concrete block external leaf, 140mm cavity with 90mm Quinn insulation and 150mm Quinnlite inner leaf, plastered internally?

Even if you build the cavity wall with insulated plaster board internally, you will still need to plaster the block work before fixing the insulated plaster board to create an airtight layer. Insulated plasterboard on block work (with no plaster) in not air tight.

hexosan

Bubbling wrote: »

What about using a 100mm concrete block external leaf, 140mm cavity with 90mm Quinn insulation and 150mm Quinnlite inner leaf, plastered internally?

Even if you build the cavity wall with insulated plaster board internally, you will still need to plaster the block work before fixing the insulated plaster board to create an airtight layer. Insulated plasterboard on block work (with no plaster) in not air tight.

You have to do the costings as quinnlites are nearly 4 times the price of standard blocks for the 100mm don't have the price of the 150mm to hand. They are also a nightmare to fix into after and need special fixing which are also more expensive.

BarneyMc

hexosan wrote: »

You have to do the costings as quinnlites are nearly 4 times the price of standard blocks for the 100mm don't have the price of the 150mm to hand. They are also a nightmare to fix into after and need special fixing which are also more expensive.

Agree. They can be used at junctions very effectively to help reduce cold bridging though.

homewardbound11

Hi

I just saw the ops drawings and something I can't figure out is the on the inner leaf 100 or 215 blocks. Isn't there a massive heat sink /thermal loss to the slab foundation.

Its just something I noted in my home where one small section is block. The rest of the home is timber frame. This section is colder than any other part of the home. I have put bit down to the inner leaf sitting on the raft foundation.
Could it be possible to use Quinn lite blocks on the first layer. Enginners report probably needed on the n strenght of the blocks.
Any thoughts.

BarneyMc

homewardbound11 wrote: »

Hi

I just saw the ops drawings and something I can't figure out is the on the inner leaf 100 or 215 blocks. Isn't there a massive heat sink /thermal loss to the slab foundation.

Its just something I noted in my home where one small section is block. The rest of the home is timber frame. This section is colder than any other part of the home. I have put bit down to the inner leaf sitting on the raft foundation.
Could it be possible to use Quinn lite blocks on the first layer. Enginners report probably needed on the n strenght of the blocks.
Any thoughts.

You'll need engineer's approval but I used a couple of layers of lite blocks at precisely this point to reduce the cold bridge.

hexosan

You normally use two rows of Quinnlite's starting off. There isn't an issue with strength as there come in 3,5&7N strength.
Namely a B3 B5 & B7 block