Wall construction

mrsWhippy

Hi there,

I'm looking for feedback and info on a couple of points regarding wall construction.

Our architect has suggested that a 150mm full fill cavity is, in his experience, the most cost-effective solution for good thermal performance.

Our Part L report has a (suggested?) U-Value of 0.20, which I can't help feeling is high for the standards achievable at the moment.

-Is it possible to achieve a better value than 0.2 using 150mm full fill cavity construction? Or is it preferable to go for a wider cavity?

-Assuming an inner leaf of 100mm, would this (typically, I know I can't get structural info here) support concrete slab on the FF, or would we have to go thicker? Architect mentioned 225mm potentially, but I have read that 100mm might be possible. Are we looking at a much more expensive build in that instance, and would we lose internal space also? I really like the idea of concrete on the FF but I don't think our architect is too enthusiastic!

This is such a minefield. Thanks!

Gumbo

mrsWhippy wrote: »

Hi there,

I'm looking for feedback and info on a couple of points regarding wall construction.

Our architect has suggested that a 150mm full fill cavity is, in his experience, the most cost-effective solution for good thermal performance.

Our Part L report has a (suggested?) U-Value of 0.20, which I can't help feeling is high for the standards achievable at the moment.

-Is it possible to achieve a better value than 0.2 using 150mm full fill cavity construction? Or is it preferable to go for a wider cavity?

-Assuming an inner leaf of 100mm, would this (typically, I know I can't get structural info here) support concrete slab on the FF, or would we have to go thicker? Architect mentioned 225mm potentially, but I have read that 100mm might be possible. Are we looking at a much more expensive build in that instance, and would we lose internal space also? I really like the idea of concrete on the FF but I don't think our architect is too enthusiastic!

This is such a minefield. Thanks!

I personally wouldn't bear a FF concrete slab on 100mm block work, I'd want 215mm on the flat at the very least.

BarneyMc

A wall U-Value of 0.20 is a very poor target in this day and age. If going 150mm cavity then most people use internal insulated plasterboard also to improve the performance. For new builds wide cavity is much better.

It's up to your engineer to specify structural details but as far as I know the vast majority of standard cavity walls use a 100mm block to support concrete FF. For my 250mm cavity my engineer stated I use a 6 inch block on the GF. Spans, etc. also come into play I guess but that's the engineer's job.

Whatever you go for allow for this in your drawings so there is no reduction in room sizes.

mrsWhippy

BarneyMc wrote: »

A wall U-Value of 0.20 is a very poor target in this day and age. If going 150mm cavity then most people use internal insulated plasterboard also to improve the performance. For new builds wide cavity is much better.

Is that what dry-lining is? Am not really keen on that idea.

Will wide-cavity increase the costs dramatically, given we need those longer ties etc? So is the idea behind a wider cavity just giving you more space for more insulation?

JimmyMW

mrsWhippy wrote: »

Is that what dry-lining is? Am not really keen on that idea.

Will wide-cavity increase the costs dramatically, given we need those longer ties etc? So is the idea behind a wider cavity just giving you more space for more insulation?

Have you actually costed it? People often state the cost of the wall ties and that they are 3 and 4 times the price of standard ties, while this is true you don't actually use a massive amount of them therefore its not a huge cost on the entire project. I am currently doing two houses with a 200mm cavity and to the best of my knowledge the wall ties for both houses cost me just over €1k inc VAT so your only talking €000's in reality. You will spend a lot more slabbing inside a block.

mrsWhippy

JimmyMW wrote: »

Have you actually costed it? People often state the cost of the wall ties and that they are 3 and 4 times the price of standard ties, while this is true you don't actually use a massive amount of them therefore its not a huge cost on the entire project. I am currently doing two houses with a 200mm cavity and to the best of my knowledge the wall ties for both houses cost me just over €1k inc VAT so your only talking €000's in reality. You will spend a lot more slabbing inside a block.

No, haven't costed it yet. I'm trying to investigate my options before paying a QS to cost up a build method that may be out of date, or not going to give us the best bang for buck.

Do people generally fully fill those wider cavities too? Are they those slabs of insulation or beads?

Thanks

JimmyMW

mrsWhippy wrote: »

No, haven't costed it yet. I'm trying to investigate my options before paying a QS to cost up a build method that may be out of date, or not going to give us the best bang for buck.

Do people generally fully fill those wider cavities too? Are they those slabs of insulation or beads?

Thanks

Full full beads is what would be used in that situation. In my research anything over 200mm cavity is where the big difference in costs come in. Please note it is the cost of the materials and the labor as a block layer will charge you more per block for anything over a 200mm cavity as it is impossible to lay from one side, therefore its much slower for them.

Please also note a cavity over 150mm needs to be designed by an engineer, you may need a block on flat in the inside depending on house design etc. Obviously this could affect the cost also

BarneyMc

mrsWhippy wrote: »

Is that what dry-lining is? Am not really keen on that idea.

Will wide-cavity increase the costs dramatically, given we need those longer ties etc? So is the idea behind a wider cavity just giving you more space for more insulation?

It's probably cheaper than dry lining and much better. Yes, wider cavity = more insulation. It also leaves your interior walls nice and solid so more thermal mass.

Anyway, I think you should be insisting on a wall UValue much, much better than 0.20. 0.12 or thereabouts is easily achievable.

thatslife

I'm in the middle of all this at the minute too mrsWhippy. As per my Preliminary BER report, going from a 0.16 to 0.14 wall will only save me 25e on heating costs per year in a 2500sqft house. I was surprised that it was that little but this is his job/calculations. He recommends a partial fill cavity.
I found a product called Xtrowall from xtratherm. 110mm solid insulation with a 40mm cavity needed. This means I dont go over the 150mm cavity with engineering sign-offs needed and I get a wall with a Uvalue of 0.15.
For me it ticks all the boxes. But a little extra cash into air tightness.

air

That sounds good thatslife but the performance of partial fill boards is predicated on impeccable build quality - smooth outer face of inner leaf, no mortar snots on the wall ties, perfectly fitted boards and a clean cavity. Personally I'd be inspecting the blockwork daily.

Johnnyhpipe

The practicality of craning a heavy precast slab and landing it onto a 100mm block wall... Personally I'd never specify this - I doubt your engineer will either.

JimmyMW

thatslife wrote: »

I'm in the middle of all this at the minute too mrsWhippy. As per my Preliminary BER report, going from a 0.16 to 0.14 wall will only save me 25e on heating costs per year in a 2500sqft house. I was surprised that it was that little but this is his job/calculations. He recommends a partial fill cavity.
I found a product called Xtrowall from xtratherm. 110mm solid insulation with a 40mm cavity needed. This means I dont go over the 150mm cavity with engineering sign-offs needed and I get a wall with a Uvalue of 0.15.
For me it ticks all the boxes. But a little extra cash into air tightness.

I would suggest costing this before committing to it as there are massive price differences between pumped insulation and board insulation, both achieving the same U Value of course

mrsWhippy

JimmyMW, is pumped insulation more cost effective? What about the risk of settling? Is that an issue these days?

JimmyMW

mrsWhippy wrote: »

JimmyMW, is pumped insulation more cost effective? What about the risk of settling? Is that an issue these days?

In my opinion it is but only marginally more cost effective, all things considered, foundations rising walls etc. The main reason I picked this method is the installation, even with the best will in the world fitting the board insulation will result in gaps and essentially a break in the thermal envelope.

In saying that pumping must be carefully installed also so as to get no breaks in the thermal envelope, however you can use a thermal imaging camera after installation to identify any gaps and then rectify it.

No the beads are now pumped in with a form of a resin which will set in the cavity essentially making the whole insulation layer one board of insulation, or at least thats the theory.

stickybookmark

JimmyMW wrote: »

In saying that pumping must be carefully installed also so as to get no breaks in the thermal envelope, however you can use a thermal imaging camera after installation to identify any gaps and then rectify it.

.

Would I be right in saying that can only be used during a certain time of the year? Something to do with the temperature outside or the heating being on?

Mrswhippy I put concrete slab FF on top of block on edge/100mm in my house. There was a difference of opinion between the arch tech and the engineer and the builder about it but in the end we went for inner and outer leaf 100mm (150mm cavity pumped beads).

Some of the internal GF walls are block on flat/215mm that would be the ones that have concrete slabs resting on them from both sides.

BER spec: GSHP, MVHR, Wall U-value 0.2

Aiming for an A2 rating

mrsWhippy

stickybookmark wrote: »

Mrswhippy I put concrete slab FF on top of block on edge/100mm in my house. There was a difference of opinion between the arch tech and the engineer and the builder about it but in the end we went for inner and outer leaf 100mm (150mm cavity pumped beads).

Some of the internal GF walls are block on flat/215mm that would be the ones that have concrete slabs resting on them from both sides.

BER spec: GSHP, MVHR, Wall U-value 0.2

Aiming for an A2 rating

Interesting. What airtightness are you going for?

Our provisional BER is only giving us an A3 - the DEAP values for the walls are 0.2, includes MVHR, A2W heat pump and Airtightness of 3 m3/(hr.m2) (both of which I think are too high)

JimmyMW

stickybookmark wrote: »

Would I be right in saying that can only be used during a certain time of the year? Something to do with the temperature outside or the heating being on?

Mrswhippy I put concrete slab FF on top of block on edge/100mm in my house. There was a difference of opinion between the arch tech and the engineer and the builder about it but in the end we went for inner and outer leaf 100mm (150mm cavity pumped beads).

Some of the internal GF walls are block on flat/215mm that would be the ones that have concrete slabs resting on them from both sides.

BER spec: GSHP, MVHR, Wall U-value 0.2

Aiming for an A2 rating

Yes a temp difference would need to be achieved between the internal and external atmosphere. Therefore during warm weather it most likely would not be suitable id imagine. However heating would not need to be installed as a blow heater with a generator could provide the heat source for the test.

thatslife

If you have proper blocklayer who builds with the solid insulation right, use cavity closers at windows/doors, you'll have a good envelope. No messing and wondering if beads are there or not.
Both methods, if done right, do the same job but beads do need a wider cavity + foundation. With UFH you want to keep that inner leaf bare from insulation too.

BarneyMc

thatslife wrote: »

With UFH you want to keep that inner leaf bare from insulation too.

Can you explain?

thatslife

Barney I think you mentioned this earlier in thread about thermal mass for heat storage. Insulating the inner leaf will counter this. So ideally for an under floor heated house, you want all your insulation in the cavity or externally.

BarneyMc

thatslife wrote: »

Barney I think you mentioned this earlier in thread about thermal mass for heat storage. Insulating the inner leaf will counter this. So ideally for an under floor heated house, you want all your insulation in the cavity or externally.

OK, thanks. Just didn't understand what you meant by that.

stickybookmark

mrsWhippy wrote: »

Interesting. What airtightness are you going for?

Our provisional BER is only giving us an A3 - the DEAP values for the walls are 0.2, includes MVHR, A2W heat pump and Airtightness of 3 m3/(hr.m2) (both of which I think are too high)

Q50<3m3/m2hr
N50<3ACH

MicktheMan

stickybookmark wrote: »

Would I be right in saying that can only be used during a certain time of the year? Something to do with the temperature outside or the heating being on?

You are correct that a temperature differential is required. However, if a heat source is available, then it is possible at any time of year (in warm months, think very very early morning surveys, just after dawn)

MicktheMan

mrsWhippy wrote: »

Our provisional BER is only giving us an A3 - the DEAP values for the walls are 0.2, includes MVHR, A2W heat pump and Airtightness of 3 m3/(hr.m2) (both of which I think are too high)

stickybookmark wrote: »

Q50<3m3/m2hr
N50<3ACH

Folks, why so poor airtight targets for newbuilds?

mrsWhippy

MicktheMan wrote: »

Folks, why so poor airtight targets for newbuilds?

That's not my target! Its just the value entered by our BER guy into the DEAP software - not sure why he entered that when we discussed getting a higher target. I'd be thinking along the lines of sub 2 but I'm not really that clear on the effort required to improve on that further versus additional costs at this stage.

stickybookmark

MicktheMan wrote: »

Folks, why so poor airtight targets for newbuilds?

Cost/complexity of achieving a higher spec versus energy bill gains. I'm not sure the gains will be worth the effort

sydthebeat

MicktheMan wrote: »

Folks, why so poor airtight targets for newbuilds?

from a purely DEAP point of view, the lower the air tightness value the lower the energy offered from renewable sources.
so in an assessment where your borderline compliant, making the house MORE air tight leaves you not compliant.

Its a stupid ridiculous algorithm

mrsWhippy

sydthebeat wrote: »

from a purely DEAP point of view, the lower the air tightness value the lower the energy offered from renewable sources.
so in an assessment where your borderline compliant, making the house MORE air tight leaves you not compliant.

Its a stupid ridiculous algorithm

I was actually wondering about that. Is it a proportion of your energy requirements that need to be met by renewables? Or how is it calculated?

If my airtightness improves, then I assume my energy requirements will decrease - why can't I just get a smaller gas/oil boiler and still leave the same input from the renewable source?

From a DEAP point of view, when the house is actually built - is DEAP plugged in with the ACTUAL values and then we'll get our BER cert based on that?

sydthebeat

mrsWhippy wrote: »

I was actually wondering about that. Is it a proportion of your energy requirements that need to be met by renewables? Or how is it calculated?

1. If my airtightness improves, then I assume my energy requirements will decrease - why can't I just get a smaller gas/oil boiler and still leave the same input from the renewable source?

2. From a DEAP point of view, when the house is actually built - is DEAP plugged in with the ACTUAL values and then we'll get our BER cert based on that?

1. you can, the size and output of the boiler doesn't really have much impact on the assessment, only the efficiency.

2. sort of (see below). You must understand though that the requirement for a DEAP assessment before starting is completely separate from the requirement to get a BER before occupation. It is just that the same software is used to do both functions.
The prelim DEAP assessment is required under building regulation law, the BER assessment is required under SI 666 2006. two completely separate laws.

An assessor can use figures used in the preliminary assessment once signed off by teh contractor / supervisor to say that thats what was exactly installed. For example, floor insulation cant be seen on completion, so a contractors or architects letter would suffice, preferably with photos as well.
The final BER will require an on site inspection to confirm whats installed of course, and some inputs such as the air tightness result is only available after completion. If no air tightness is done, the worst default value must be inputted. this often causes the final BER to show non compliance with building regulations.

Thatsnicenow

thatslife wrote: »

I'm in the middle of all this at the minute too mrsWhippy. As per my Preliminary BER report, going from a 0.16 to 0.14 wall will only save me 25e on heating costs per year in a 2500sqft house. I was surprised that it was that little but this is his job/calculations. He recommends a partial fill cavity.
I found a product called Xtrowall from xtratherm. 110mm solid insulation with a 40mm cavity needed. This means I dont go over the 150mm cavity with engineering sign-offs needed and I get a wall with a Uvalue of 0.15.
For me it ticks all the boxes. But a little extra cash into air tightness.

Hey not an expert but I was going with an 8 inch cavity pumped originally as was builders suggestion, then engineer said he would have to increase foundation concrete and steel, looked into it in more detail and am now going with a 6 inch cavity with a 140mm extratherm tounge and groove board so will have 10mm cavity, working out as same cost as pumped cavity due to need of extra concrete and steel but much much better u value(cant remember off hand), block work will have to be tidy but am close to the site and will check it regurlarly! hearing bad stories about pumping walls with insulation ie walls not being filled fully and/or settling down after a period of time, im of the opinion theres a cavity for a reason also as regards moisture penetrating through the external leaf (i live in a very exposed costal location!)

Theimprover

Lose the cavity people, block on flat with 230mm external insulation is the way to go, it's also passive.

mrsWhippy

Theimprover wrote: »

Lose the cavity people, block on flat with 230mm external insulation is the way to go, it's also passive.

Is this generally more expensive?

sydthebeat

mrsWhippy wrote: »

Is this generally more expensive?

When you add in the warm roof construction and the favorable insulated foundation then yes, it is.

Every choice has knock on effects.

Theimprover

mrsWhippy wrote: »

Is this generally more expensive?

I was originally going with ICF but with block on flat and my 230mm external insulation I am achieving a lower U value and it is working out cheaper but off hand I cant see how it could be much more expensive. Haven't done the figures as I was never going with a cavity. I'm a builder myself so I will be able to do the external insulation myself, materials will cost for external insulation about €25 p/m2 finished.
The insulating of the foundation doesn't change. I was always using 150mm.

hexosan

Theimprover wrote: »

I was originally going with ICF but with block on flat and my 230mm external insulation I am achieving a lower U value and it is working out cheaper but off hand I cant see how it could be much more expensive. Haven't done the figures as I was never going with a cavity. I'm a builder myself so I will be able to do the external insulation myself, materials will cost for external insulation about €25 p/m2 finished.
The insulating of the foundation doesn't change. I was always using 150mm.

I call bulls*#t on this figure. There's no way you can get 230mm of external insulation and by finished I assume fixed & plastered for €25/m and without seeing the invoices proving same it's a back of a fag box calculation.

kieran.

Well EPS is about €75/m³ so that,s €17.25 per m², render system assuming its a reasonable cheap system such as webber works out at €15/m² and additional material to supply and fit (Fixings beads rails etc come in at €7) plus labour at €15.25 / m², is a total of €55 / m² these are also NETT builder prices without any loading for complexity or profit & overheads. If hes doing all the work himself I reckon closer to €40/m² would be more accurate!!

Theimprover

hexosan wrote: »

I call bulls*#t on this figure. There's no way you can get 230mm of external insulation and by finished I assume fixed & plastered for €25/m and without seeing the invoices proving same it's a back of a fag box calculation.

Call it what you want, anyway my mistake, its about €25 for 100mm and closer to €30 for 230mm, and this is materials ONLY. TBH I'm not bothered one bit what you think, I'm buying this regularly.

Just trying to give some advice to a previous posters.

Thatsnicenow

I've been quoted 36 plus vat for supply and installation of an insulation board in the cavity of the block wall of a house I'm starting to build, the board retails for 24 plus vat,can anyone here tell me is 12 plus vat a fair price for installation? It's a 140 mm tounge and grove board for use in a 6inch cavity with a u-value of 0.13 with a pvc outer coating for the moisture with fins about 10mm so fills the cavity fully when in place, I'd name the board but not sure if against the rules here. Prices per m2.

hexosan

Theimprover wrote: »

Call it what you want, anyway my mistake, its about €25 for 100mm and closer to €30 for 230mm, and this is materials ONLY. TBH I'm not bothered one bit what you think, I'm buying this regularly.

Just trying to give some advice to a previous posters.

EPS is sold by the m3 so if 100mm is costing €25 the extra 130mm (roughly 60%+ material) can't be costing €5 more.

It's annoying when people come on here and post figures that can't be backed up with fact as people read this and think it's possible, the. Get badly caught out with their budgets.

Thatsnicenow

Anyone have any thoughts on my post?

kieran.

Thatsnicenow wrote: »

Anyone have any thoughts on my post?

Fitting of the boards should be built into your blockies price along with cills, lintels, dpc's, vents etc

As an individual price I would expect to pay the same price per insulation unit as per block ie approx €1 each per unit

Assumming your fitting the product is think 1.2x0.45 I would think a price of €2-3/m2 would be cost.

Thatsnicenow

Thanks Kieran. We had originally proposed to go with pumping the cavity so builders contract was for foundations, walls and roof, so now that we've changed our mind on insulation type and builder now required to put insulation board in place, but was thinking his price of 36 plus vat was excessive when I found the price of insulation is 26 plus vat. Just want to have all the info before I speak to him about this!

Thatsnicenow

Thanks Kieran. We had originally proposed to go with pumping the cavity so builders contract was for foundations, walls and roof, so now that we've changed our mind on insulation type and builder now required to put insulation board in place, but was thinking his price of 36 plus vat was excessive when I found the price of insulation is 26 plus vat. Just want to have all the info before I speak to him about this!

Calahonda52

kieran. wrote: »

Fitting of the boards should be built into your blockies price along with cills, lintels, dpc's, vents etc

As an individual price I would expect to pay the same price per insulation unit as per block ie approx €1 each per unit

Assumming your fitting the product is think 1.2x0.45 I would think a price of €2-3/m2 would be cost.

So the implied import of the above is that it is as easy, time-wise to fix the cavity insulation, properly, allowing for the wall ties, cutting etc, as to lay three concrete blocks.
I am not a QS, but I do know bit about this, have first gone on site in 1972, and time and motion studies and I find this.....

BarneyMc

Thatsnicenow wrote: »

Thanks Kieran. We had originally proposed to go with pumping the cavity so builders contract was for foundations, walls and roof, so now that we've changed our mind on insulation type and builder now required to put insulation board in place, but was thinking his price of 36 plus vat was excessive when I found the price of insulation is 26 plus vat. Just want to have all the info before I speak to him about this!

Different brands are different prices. Is the brand of insulation specified?

Thatsnicenow

@barneymc Yes it was a specific board of a specific brand,
@calahonda52 are you in agreement with Kieran that it would cost builder approx 2-3 euro to put each m2 insulation in place?
I understand builders have to make a profit but I don't want to be taken advantage of seeing as I have little experience in building a house and will be paying for it for the next thirty years

kieran.

If you haven't started works year get two further comparison prices for the complete walling portion of your works that's the only way you'll know for sure.

Theimprover

hexosan wrote: »

It's annoying when people come on here and post figures that can't be backed up with fact as people read this and think it's possible, the. Get badly caught out with their budgets.

I'm not getting into a big debate over this but I can assure you that what I said is fact, I'm actually looking at an invoice here and without going into to much detail, 582 m2 which it is always measured in, NOT M3, cost me €17,338.77 which works out to about €29 p/m2 for 100mm EPS along with everything else needed to finish it, and this particular job had a lot of windows.