Out of my depth - Air Tightness and Insulation....

[Mulberry View]

So, I've built this with very little outside help. I'm proud to say that I'm still working within about 3-4mm of all of the plan measurements.

 

 

We have no support from our eye-wateringly expensive Architect any more, she's a Diva of the highest order with the worst temperament of anyone I have ever paid for a service, she left the project at a time when we still weren't certain of all the details.

 

I have to admit that I feel out of my depth in understanding Air Tightness detailing and Insulation/u-Value requirements. I am simply aiming to improve on as many of the Architects details as possible. but after reading some posts on here, it's clear to me that there are bods on here that put my knowledge to shame and I'm desperate to get this right.

 

Current concerns.... (not limited to)

 

The relatively weak u-Value of the Nudura. On paper, the standard system doesn't present great u-Values, though I'm told that this isn't the only thing to consider. Should I be thinking of adding further insulation to the walls? I do kinda regret not going for the heftier blocks in all honesty.

 

I'm minded to improve on the Architects spec of 150mm PIR in the floor (over Beam & Block). I have room for 200mm and am committed to that with interior FFL's now, but is it a sensible choice?

 

I'm minded to improve on the Architects spec of 120mm in the Warm Roof. Again, I have room for 200mm, but is it worthwhile.

 

I do not fully understand best practise with Air-Tight detailing, around windows/doors and so on.

 

Our Architect arranged a SAP calculation at the design stage, and we're trying to control costs of course, but should I be talking to a consultant of some sort about this stuff? I would like to aim for 'near Passivehaus' levels and I'm not thinking as much about all-out return on investment but more having a comfortable home with as low as possible need for heating input. What's the best way to approach this?

[Mr Punter]

@Russell griffiths has built with Nudura and knows his onions.

[Redbeard]

Re the roof, yes, go for more. 120 is very borderline. I would put more in a refurb roof. Are you building the roof or others? The thicker the insulation the harder it is to find the timbers with your HUGE screws! I have seen a warm roof where most of the fixings were to the under-layer of 18mm OSB, not to the timbers.

[Nick Laslett]

Here are some useful threads, that you might have already seen. 
 

 

This is the one where Russell talks about using Triton TT Vapour membrane paint for prepping his window reveals. 
 

 

You have already seen this one about ICF and windows.  There is a link in this thread to another thread about ICF windows. 
 

My ICF build is 9 miles from Diss, you’re welcome to come and visit for chat. Just send me a private message 

 

Edited February 14 by Nick Laslett

[Redbeard]

Re air-tightness, ultimately everything wants to connect to everything else! So if the internal plaster is the A/T layer, floor membranes want to connect and be taped. Ditto windows. Have you got your ground-1st floor detail sorted.? Search for 'Tony trays' if not.

[SteamyTea]

Thermal engineering of a house is pretty basic.

Stop warm air leaving, stop cold air getting in.

All that means is the outside of the house has to stop air movement, not the inside as that can allow the insulation to be cold.

 

Don't let anything that conducts heat better than the insulation go from inside to outside i.e. beams and joists.

 

Control the internal humidity, this is usually done mechanically l.e. a fan and ducts.

Any humidity that does manage to get past the vapour control layers (basically a sheet of polystyrene in the inside walls) must be allowed to migrate to the outside. This is why walls are constructed so that the more vapour tight layers are inside, and the more vapour open layers are outside.

 

Vapour movement and air movement are not the same thing. 

 

Sealing around window and door frames is a matter of taping either side ideally.

Window and door frames are also thermal bridges, i.e. they conduct heat better than the walks, which is a bad thing. 

The better the frame U-Value the better, but be conscious that large windows have poor thermal performance anyway, so the frame may only be a small part of the overall heat loss.

 

You can swap around U-Values i.e. thicker insulation on a north and east facing wall, these are climatically colder in the UK, and still get a well performing house.

 

Your most likely to have overheating problems than under heating problems these days, even sticking to minimum building regulations. Do so thermal modelling i.e. solar angles, intensity at different times of the day and year. This only needs to be basic, split the day up into 18 hours, 9 either dude if noon, split the year up unto 26 weeks, then go to PVGIS and download the TMA hourly data for your location.

 

Edited February 14 by SteamyTea

[saveasteading]

There are diminishing returns with insulation thickness. The building regulations and manufacturers don't acknowledge it though.

But it is the case, especially with varying heating patterns. 

So I'd maybe put 50mm of eps on the bottom as it's half the price of PIR. Half as good in theory too but i think it is the pragmatic solution, especially as the outside is never far away with your layout.

But air-tightness is crucial, and just needs attention to detail. so I'd take up that offer of tuition.

[saveasteading]

I'm assuming underfloor heating! Hence slab insulation is more effective than the other locations.

 

[Meabh]

ICF superstructure built by our supplier, Internorm windows also fitted by them. I've been in charge of local trades since structural shell completion (apart from the windows). Lots of windows, high ceilings. Didn't trust others to do airtight tape and with 3 kids we'd never have managed it in time. I used Aerobarrier in Jan (just before plasterboard) who do an airtight spray (and foam up any big holes). They got us from 4.29 ACH to 1.33 with a temp front door and big sliders missing silicon (taped only). This was also pre plaster and pre render. The spray plugged gaps in areas I wasn't expecting e.g between the glass and frame of some of our Internorm fixed windows!!

 

They can do you a quote with plans/elevations and then compare that cost to the airtight tape. For the shell stage it was pretty similar!

[Buzz]

1 hour ago, saveasteading said:

So I'd maybe put 50mm of eps on the bottom as it's half the price of PIR. Half as good in theory too but i think it is the pragmatic solution, especially as the outside is never far away with your layout.

Or just put 200mm of eps in the floor , much cheaper than pir will give a similar u value to 150mm pir and you won't have to make up the 50mm with another layer of something. 

[saveasteading]

2 minutes ago, Buzz said:

much cheaper than pir will give a similar u value to 150mm pir

I think it is half the price and half the insulation in rough terms. But i could be persuaded to 100eps on the bottom and 50pir on top. Staggered laps are a very good thing anyway.

[Buzz]

36 minutes ago, saveasteading said:

I think it is half the price and half the insulation in rough terms. But i could be persuaded to 100eps on the bottom and 50pir on top. Staggered laps are a very good thing anyway.

Decisions Decisions at this stage and would need to see the calculations for performance vs cost before i made a choice, we opted for 175mm of eps 100mm then 75mm Cross lapped for a u-value of .12 but our is 300m2 and fairly square 

[Jenki]

3 hours ago, Buzz said:

Or just put 200mm of eps in the floor , much cheaper than pir will give a similar u value to 150mm pir and you won't have to make up the 50mm with another layer of something. 

 

2 hours ago, Buzz said:

Decisions Decisions at this stage and would need to see the calculations for performance vs cost before i made a choice, we opted for 175mm of eps 100mm then 75mm Cross lapped for a u-value of .12 but our is 300m2 and fairly square 

I had the luxury of 300mm depth of insulation, so opted for 300mm EPS equivalent to 150PIR  . I used some EPS 150 for the top layer and EPS70 for the layers below, staggering the sheets as I went. (this was a cost based decision) Ultimately your injecting heat into the concrete and this insulation is the only thing stopping you heating the earth, or conversely the earth cooling your slab.  150mm PIR will give you good results, but if you have space it cant hurt, other than financially, to put more insulation in there.   

Note: if you are doing 150mm, don't be tempted to just buy the 150 sheets, they are PITA to cut neatly and you wont be able to stagger the joints. Thinner sheets will cut accurately (but messily) on a table saw. 

@Mulberry View keep the faith its looking good 👍.

I say  Mandy and I, built our house on our own, with very little external help, but the reality is, it was Mandy, Me and Build hub.  Hours spent on here reading blogs, questions and asking for clarification on bits your not sure of will save you lots of headaches down the line and then end product, IMHO will outshine many homes.

 

[Mulberry View]

On 14/02/2024 at 17:41, Redbeard said:

Re the roof, yes, go for more. 120 is very borderline. I would put more in a refurb roof. Are you building the roof or others? The thicker the insulation the harder it is to find the timbers with your HUGE screws! I have seen a warm roof where most of the fixings were to the under-layer of 18mm OSB, not to the timbers.

 

I have a Zinc contractor who is insistent on laying the insulation. It's going over 22mm of Class 3 Plywood (specified by the Architect?). I will check with the contractor how he feels about going over 200mm of insulation, but I think I've mentioned it already.

[Mulberry View]

On 14/02/2024 at 17:51, Nick Laslett said:

Here are some useful threads, that you might have already seen. 
 

 

This is the one where Russell talks about using Triton TT Vapour membrane paint for prepping his window reveals. 
 

 

You have already seen this one about ICF and windows.  There is a link in this thread to another thread about ICF windows. 
 

My ICF build is 9 miles from Diss, you’re welcome to come and visit for chat. Just send me a private message 

 

 

Excellent reply, thank you. I'll get into those topics soon.

 

I'd love you see your build, I'll drop you a message.

[Mulberry View]

On 14/02/2024 at 17:54, Redbeard said:

Re air-tightness, ultimately everything wants to connect to everything else! So if the internal plaster is the A/T layer, floor membranes want to connect and be taped. Ditto windows. Have you got your ground-1st floor detail sorted.? Search for 'Tony trays' if not.

 

My Posi Joists sit within the ICF walls as opposed to on top of them and the Plywood layer oversails onto the wallplates, in my head this feels like a good start with being able to airtight the roof junction, though I'm not certain how that will occur.

 

Ultimately, I do have it in my head to place a 50mm service void under the roof to enable me to get most of my electrics etc inside the the airtight envelope, which I also gather is a good idea.

 

I have first floor structure in the works, as can be seen here. The penetration to the inner skin for this is minimal. You'll also see in that thread that I have passed Zehnder Comfopipe lengths through and cast them in concrete so they ought to be fully airtight already?

 

 

[Mulberry View]

On 14/02/2024 at 18:02, saveasteading said:

I'm assuming underfloor heating! Hence slab insulation is more effective than the other locations.

 

 

Yes UFH. One of the major appeals to us wanting to build a house is to have warmth underfoot (and no condensation! something we lived with for years).

[Mulberry View]

On 14/02/2024 at 18:10, Meabh said:

ICF superstructure built by our supplier, Internorm windows also fitted by them. I've been in charge of local trades since structural shell completion (apart from the windows). Lots of windows, high ceilings. Didn't trust others to do airtight tape and with 3 kids we'd never have managed it in time. I used Aerobarrier in Jan (just before plasterboard) who do an airtight spray (and foam up any big holes). They got us from 4.29 ACH to 1.33 with a temp front door and big sliders missing silicon (taped only). This was also pre plaster and pre render. The spray plugged gaps in areas I wasn't expecting e.g between the glass and frame of some of our Internorm fixed windows!!

 

They can do you a quote with plans/elevations and then compare that cost to the airtight tape. For the shell stage it was pretty similar!

 

Yes, I've seen Aerobarrier. Luckily my 'kid' is all grown up and not biting at our ankles. Well, actually that's a lie. At 29 years old, she's more dependent that ever, but that's how it goes!

 

Did you do Airtesting after the wet trades? I'd love to know what Aerobarrier costs. I feel as though the cost will be linked to the result it brings and not to the amount of work in applying it. I'm shocked to hear of your unexpected air 'leaks', particularly the windows.

[Mulberry View]

On 14/02/2024 at 19:11, Buzz said:

Or just put 200mm of eps in the floor , much cheaper than pir will give a similar u value to 150mm pir and you won't have to make up the 50mm with another layer of something. 

 

I had presumed we'd fit 200mm of PIR. Keep in mind I haven't costed this up yet, so that might be where that decision changes.

 

Budget is a whole other conversation, we're winging it in that regard too, though think we're doing OK so far. No spreadsheet!

[Chanmenie]

30 minutes ago, Mulberry View said:

 

I had presumed we'd fit 200mm of PIR. Keep in mind I haven't costed this up yet, so that might be where that decision changes.

 

Budget is a whole other conversation, we're winging it in that regard too, though think we're doing OK so far. No spreadsheet!

I fitted 200mm PIR in the floor under the UFH and 205mm in the roof 

You could also add insulation to the Nudura if the U values are not great.

What are the U values for your blocks

[Mulberry View]

15 minutes ago, Chanmenie said:

I fitted 200mm PIR in the floor under the UFH and 205mm in the roof 

You could also add insulation to the Nudura if the U values are not great.

What are the U values for your blocks

 

Similar insulation levels to what I'm proposing then.

 

The quoted u-value for the Nudura standard blocks is, I believe, 0.24, though I am told that things aren't this simple and that the individual components of the wall should be calculated and that the concrete brings its own advantage.

 

In fact it was the relatively poor u-value that came to my realisation when Total Home Environment pointed it out as being probably the sole reason for my 'C' as designed SAP score. With that said, the as-designed SAP has window, insulation and air-tightness values that are easy to exceed.

[Jenki]

1 hour ago, Mulberry View said:

The quoted u-value for the Nudura standard blocks is, I believe, 0.24

In Scotland this would not pass building control, 0.18 is the maximum. My ICF (polysteel), needed EWI and then the standards changed in early 23 so needed 25mm PIR IWI that got me down to 0.139. 

We've spent the best part of 2 months in our home now, and very happy with the ICF decision.

DHW and heating  220kWh for January and it's been cold and wild at times.

Push for decent  insulation levels, but use the heat loss calculation spreadsheet to play with the figures. It's very apparent that air tightness becomes more important once you've got a decent level of insulation..

[Chanmenie]

Yeah 0.24 doesn’t sound great, I used Beco Wallform 375 which is quoted at 0.14 

so the PIR  200 floor and 205 roof should get me to passivehaus standard 

[saveasteading]

The best thing I have learnt on BH is to build a service void inside the walls. Benefits in airtightness and happy service contractors. But it also adds insulation in itself from the basic air gap and surface benefit, to any amount of additional insulation you wish.

[Post and beam]

12 hours ago, Mulberry View said:

I'd love to know what Aerobarrier costs.

I very recently had a price of £2200 for my Potton 200 sq metre project in North Herts.  They did say that they would stay and keep spraying until we got the airtight figure we needed/wanted. I think i will be taking them up on this offer.