Least Expensive Building Methods to Meet Current Standards

redsheeps

We're getting construction drawings completed at the moment. We informed the architect of our budget and they've advised certain building methods. I touched base with a couple of builders and they've all told me the architects suggestions are crazy expensive and unnecessary.

With regulation now the house has to be A2 rated. The architect is recommending the whole house is built using thermal lightweight blocks and external insulation. All the builders said this was completely unnecessary, particularly the lightweight blocks and will annihilate the budget - they all said these blocks are only needed at certain specific spots of the house for reducing thermal bridging and not the whole house. They all consistently said the external insulation was also the most expensive way to insulate the house, that it's almost exclusively used for retrofits rather than new builds and that, if we are trying to keep things to a budget, advised cavity insulation with/without internal insulation.

We're trying to get a handle on this now before signing off on the construction drawings / tender documents. We don't care about any fancy building methods, the house is a standard enough ~200sqm country house (no big glass, no funny angles, etc.). We've generally been advised to go with air-to-water, heat recovery system, underfloor heating, concrete floors on 1st floor to support the under floor heating and sound insulation. Outside of this list we just want to 'basic' spec that will get us to A2 rated.

Are there any glaringly obvious building methods that we should avoid or include to keep costs down?

TimHorton

https://www.boards.ie/discussion/2058316248/new-build-external-wall-insulation#latest Have a read of this .

Ronney

Maybe employ a QS to get it on budget? Have you looked at options like Timber frame?

Calahonda52

They all consistently said the external insulation was also the most expensive way to insulate the house, that it's almost exclusively used for retrofits rather than new builds and that, if we are trying to keep things to a budget, advised cavity insulation with/without internal insulation.

Complete boxxol but it comes from the we always did it this way stable of DUP-esque intransigence to change.

You will also find this BS when it comes to setting airtightness targets in the contract.

Have you seen the dwelling report from the BER software ?

what are the component U values that arrive at the A2 or is it being fuzzed with PV?

The issue here is the EWI is looked at in isolation as is the CWI and IWI, whereas you need to look at the entire cost of the thermal envelope element,the wall in this case, the U value achieved and the lifetime energy saving of each construction.

The other issue is that as its pretty easy to get a U value of 0.15 with EWI, at maybe 250/300 euro for a sq m then this reduces the pressure on the other thermal fabric components to make sure the A2 is met, maybe requiring triple G windows, best U value about 0.75 [ 5 times worse than the wall at .15, at 1750 2000 euros a sq m

Re the thermal blocks, will they take the weight of the hollow core

dbas

https://www.boards.ie/discussion/2058322142/least-expensive-building-methods-to-meet-current-standards

Thermal blocks everywhere is madness. Look up acceptable construction details in technical guidance document part L. Any construction method that uses those details with a very airtight fabric will do the trick. You'll notice a thermal block in the concrete details if you look.

Really good airtightness with heat pump and mvhr. Blowerproof works really well sprayed on concrete blocks.

You don't need an A2 either. It'll tell you in tgd part L that you need EPC below 0.3, CPC below 0.35 and rer greater than 0.2

SIP is quite expensive in materials but saves a lot on labour. Done properly the fabric is airtight without all the expensive membrane and most of the taping.

redsheeps

@TimHorton Sound for the link. That person's approach looks very similar to the architect's recommendation. That person's father is a bricklayer who's comfortable to take on that approach. We've spoken to five builders who all, bar one, has never done the EWI. The architect did say we'd need to source a builder who is comfortable with the approach we're considering, and that's been very difficult.

https://www.boards.ie/discussion/comment/121367365#Comment_121367365

We considered this. We realise the potential loss in not employing one, but we've gotten quotes in the region of €7k for this. There are so many thousands going out before a block is laid it's been difficult to ascertain what is and isn't needed. Architect said one off builds don't go the QS route as the builders it's sent to tender have QSs for this. It seems a bit cart before the horse though as we have to agree on the construction method before tendering.

We considered timber frame. Visited one crew and spoke with another. They both said not to expect any financial saving going timber versus block. Only saving with timber is a time saving. We also struggled to get a builder/contractor familiar with taking on the remaining works after the main timber structure is erected. We asked for names and all the timber crews could give us were self-build people and we don't want to go self-build.

https://www.boards.ie/discussion/comment/121368649#Comment_121368649

I can see from some of your other posts you know about insulation. We've gotten the sense that the builders are very familiar with the cavity approach + internal insulation and that is the major reason they're recommending it. We're working to a budget, and I think you've hit the nail on the head with things being how they've always been done so there's a familiarity with it. We've gotten pre-construction drawing ballpark estimates per m2 for platinum cavity and they're in budget for us and BER guys have advised it will reach A2 requirement at 125-150mm cavity + maximum 62.5mm internal insulation.

I think the crux of it for us is the recommended builders who have the time to take on the work have all, bar one, never done EWI. The architect did say we'd really need to source a builder who is confident and familiar with the build process going single leaf with EWI. The one that did use it once said it only got the house an A2 rating anyway (now obviously other factors play into those ratings than just wall insulation), it marks with kids hitting things off it, and they'd have to sub-contract out the work as they have no experience installing it themselves.

BER guys I linked with said the condensation and mould with cavity + internal insulation happens when people put too much internal insulation on the house. Advised 62.5mm as a maximum internal insulation and if we stay to that thickness or thinner, we won't have the condensation and mould issue. We have family who built approx. 10 years ago using cavity + internal, and they've no condensation or mould issues.

https://www.boards.ie/discussion/comment/121368700#Comment_121368700

Air tightness with heat pump and MVHR are what we're going for, and the air tightness in particular was what the builders all said was key to the process as well. At least there's consistency in that recommendation!

https://www.boards.ie/discussion/comment/121368724#Comment_121368724

We considered alternative build methods, but we're working to a time frame and we just want to stay with what is typical. Cheers for the suggestion though.

Scoopsire

Have none of the builders/architect suggested a wider cavity with no internal insulation?

Btw how much is the platinum bead working out per sq meter?

Would you mind sharing the details of the timber frame companies you spoke to please via PM?

redsheeps

https://www.boards.ie/discussion/comment/121372976#Comment_121372976

They have but I can't remember the specifics. The max recommended by architect, builder, and BER crews was 150mm. I think it was something structural that creates difficulties with wider than this - but I do remember the architect saying it could be done but would require a full re-working of construction drawings.

I haven't gotten QS level quotes from the builders, just initial ballpark figures for our house size with the finish we're seeking. Approx. 180-190 per sqft.

Will PM the names no problem.

Calahonda52

https://www.boards.ie/discussion/comment/121373447#Comment_121373447

Wider than 150 requires structural design sign off and more expensive ties and foundations.

redsheeps

https://www.boards.ie/discussion/comment/121374067#Comment_121374067

That was it!

Curious if you've any experience with the recommendation about 150mm cavity bead with max 62.5mm internal insulation? Was recommended as the way to go to prevent the condensation and mould concerns people have about going with cavity insulation.

Calahonda52

Condensation and mould is a multifaceted and complex issue which defies sound bites!, so I don't buy that soundbite.

For the record I despise cavity wall construction and utterly despise cavity walls with insulated cavities.

In general terms The issue at play here is where is the dew point in relation to the vapour barrier?

This gives rise to what is sometimes called the 2/3rd rule which suggests that 2/3rd of the thermal conductivity of the insulation should be outside the vapour barrier so as the dew point stays outside the vapour barrier

Its important to note that its not 2/3 of the thickness unless the thermal conductivity of the insulation on both sides is the same.

Isn't the best solution to condensation and mould to keep relative humidity as low as possible within the living envelope. Some sort of ground up mechanical ventilation system into every room thought about as part of the design phase. Building regs do not specify this so there is little point in seeking wisdom there.

Furze99

https://www.boards.ie/discussion/comment/121374973#Comment_121374973

"For the record I despise cavity wall construction "

That's surely a fairly big statement against a proven form of construction that has been widely specified & used in the last 50 years?

Me, I'd rather have a properly built cavity wall with two leaves of standard blocks, with air gap and properly fitted snug insulation against inner leaf - than any of your timber frame or EWI or whatever constructs. In terms of solidity, substance, longevity as well as performance. When I was building such here, I made it my business to look at various houses under construction, at various stages of build. Saw everything from excellent detailed work to downright shoddy stuff. Surely the OP needs a competent builder, if those available are familiar with this method and their work is of a high standard, that's the way to go. Also to OP, check out real house owners experience with EWI in terms of durability and toughness.

dbas

Not trying to steer you in any direction here, but some suppliers calculate the thermal bridges for construction details. Mannok being one, but there are others. Google is your friend

https://www.mannokbuild.com/accredited-construction-details/

Take a look at the details and think about them in relation to your own build.

Getting these details right and using them exactly as per the detail would likely allow you to use the max allowable u values in your build, which will save you money.

You need solid evidence of using these and your BER assessor will tell you what they need.

Calahonda52

https://www.boards.ie/discussion/comment/121376668#Comment_121376668

to move away from default thermal bridging values in the BER needs specialist NSAI registered folk

dbas

https://www.boards.ie/discussion/comment/121378527#Comment_121378527

Those values are from nsai registered folk