How to make area behind skirting board airtight

[garo99]

We redid our kitchen last week and I took the opportunity to get some PIR boards installed internally on all the external walls (concrete block) before the kitchen cabinets went on. When the plastering was done, the plasterer left an inch gap at the bottom (Floor is tiles on concrete) - I presumed this was customary for the skirting boards to go back on. However, I can feel a draught on the bottom of the external wall behind the sink and I presume there is some air leaking in all along the floor. Some of this is not behind kitchen cabinets so sadly out of reach but there are still sections I can get at.

 

The worktop goes on in a week and the man who did the plastering is coming back in on Tuesday. Is there anything I can ask him to do to fix this? Airtight tape? Expanding foam? I don't think replastering the last inch is an option. I wish I had got them to plaster to the tiles at the start.

 

I am hoping to go MVHR at some point so improving airtightness is something I want to do.

[nod]

Use BLUE expanding foam on the areas that you can get at 

 

[Nickfromwales]

I use Illbruck 330 airtight foam, very good stuff and far more robust than you typical open cell foam.  
 

https://sealantwholesale.com/products/illbruck-fm330-pro-foam?variant=43795891683555&currency=GBP&utm_medium=product_sync&utm_source=google&utm_content=sag_organic&utm_campaign=sag_organic&gad=1&gclid=EAIaIQobChMI_uvl38WzgQMVF4btCh3aDggcEAQYAiABEgIvuPD_BwE

 

If you are considering MVHR then you will need to do a blower test first, because if you have natural infiltration (a crafty house) in excess of 1 ACH then MVHR will be useless unless the fan speeds are high and that means a noisy (audible) system which will have quite poor performance for heat recovery. If you’re not recovering heat, then you have just bought and installed a system that introduces cold air in the winter whilst simultaneously flushing out to the clouds all the heat you just paid to create. 
Think twice before installing and get an evidentiary air test done to see how ‘bad’ the house is, as it is likely to be north of 3-4 ACH or worse as is. Air leakage from around every window will be significant, as will the floors / joist sockets into the walls beneath the 1st floor floorboards, and also all dot & dabbed walls to the attic. Google thermal tenting, it’s a shocker where air gets to and how it carries your precious heated air away. 
Maybe book yourself in for a course or 2 at the NSBRC and go see their EnerPHit refirb house to see how airtightness can be resolved retrospectively.  

[Redbeard]

How were the boards fixed? I think I'd be asking a lot more Qs. Perhaps worst case is that they are on adhesive dabs without a full perimeter bead (meaning a risk of - cold - air movement between wall and insulation). If so the best you can hope to achieve (without taking it off again) is perhaps to drill a series of 10mm holes at say 40 - 50mm centres and gun in Illbruck FM330. all round the perimeters. Make good with jpint filler and scrim (or ask the plasterer to do it).

[garo99]

Thanks all for your replies.
@nodCan you expand on BLUE foam? This came up on a google search: https://www.screwfix.ie/p/soudal-soudafoam-expanding-foam-gun-grade-750ml

 I am looking for something that doesn't expand a lot? Or is it the brand: https://blue-60.co.uk/

@Nickfromwales Long time lurker of the MVHR forum I know what you are talking about. We got our windows redone recently and are slowly improving airtightness. The attic is a big source of heat loss and I plan to tackle that before even thinking of a blower test. This is more of an opportunistic attempt to improve what I can. As regards MVHR, I am planning to only do the upstairs bedrooms and my motivation is as much air quality as it is heat recovery.

@Redbeard The boards were attached straight onto the concrete blocks. They were screwed in using some special type of screws and not a dot and dab job. This was followed by a full plaster which I am pretty happy with. The joins were pretty tight - I checked before plaster went on - and I don't think there was a perimeter bead there wasn't much room for cold air movement between the wall and the board as the boards were fixed directly on the brick and there are no battens. I only have an issue with the bottom inch on two external walls.

[Mike]

10 hours ago, Nickfromwales said:

I use Illbruck 330 airtight foam

That would be my choice too.

[Redbeard]

So was there plaster on the wall to which the insulation boards were attached, or bare block? If the former, maybe OK (although personally I don't like trapping gypsum plaster in a 'sandwich' on the cold side). If the latter, there may be leakage. My preference is always for a parge coat (lime for me) as an air-tightness layer before insulating.

[Redbeard]

Forgot to say, where do you think the air is leaking from? Is there a ventilated suspended floor? If you are 100% satisfied that there is no air-space between board and wall then maybe you don't have to worry re that leakage cooling the whole wall. If you are that satisfied then maybe just seal the bottom of the board with FM330 (though I prefer belt, braces and other measures!) 

[Nickfromwales]

5 hours ago, Redbeard said:

maybe just seal the bottom of the board with FM330

If done meticulously the thermal tenting will be dramatically reduced. The problem for us here, is, to convey to the OP just how much work and investment goes into air-tightening a retrofit. It is a huge pursuit, and then some, but the rewards are just as big.

[Post and beam]

Just googled 'thermal tenting'. That didn't work

[Sparrowhawk]

19 hours ago, garo99 said:

Thanks all for your replies.
@nodCan you expand on BLUE foam? This came up on a google search: https://www.screwfix.ie/p/soudal-soudafoam-expanding-foam-gun-grade-750ml

That's the stuff and it doesn't expand a lot - it's well controllable. However the blue is strong - you can wipe the foam off if it goes too far but in my experience the blue colour stays forever. For this reason only I've switched to the Illbruck FM330 that everyone else mentions, despite the price/having to buy online.

[Sparrowhawk]

3 minutes ago, Post and beam said:

Just googled 'thermal tenting'. That didn't work

 

This is a better search term: https://www.google.com/search?q=plasterboard+thermal+bypass

 

Mark Siddall's guide for The Passivehaus Trust on thermal bypass risks is very much worth a read: https://www.passivhaustrust.org.uk/UserFiles/File/Technical Papers/Thermal bypass risks v1.0 222909.pdf

[AliG]

This is very interesting.

 

I have 4 large eaves spaces with PIR between the joists.

 

The architect specified airtightness membrane at the last moment to cover this. It was installed by the builder at a cost of thousands of pounds.

 

Last year I opened up the eaves and spent quite a bit of time making sure the membrane was actually airtight. For example there were many places where nails had been put through it, or it was torn.

 

However, now that it is airtight, it billows out when it is windy. I have been thinking, does this cold air getting on the inside of the PIR actually render it useless? The document there confirms my suspicions.

 

Would I in fact be better cutting off the (very expensive) membrane and taping up the PIR directly to the joists with airtightness tape?

 

The rooms with these eaves spaces take notably more heating than other rooms in the house.

[garo99]

12 hours ago, Nickfromwales said:

If done meticulously the thermal tenting will be dramatically reduced. The problem for us here, is, to convey to the OP just how much work and investment goes into air-tightening a retrofit. It is a huge pursuit, and then some, but the rewards are just as big.

 

I appreciate that. At this point I am looking for quick fixes and tidying up things that will be harder to do once the kitchen is complete.

 

17 hours ago, Redbeard said:

Forgot to say, where do you think the air is leaking from? Is there a ventilated suspended floor? If you are 100% satisfied that there is no air-space between board and wall then maybe you don't have to worry re that leakage cooling the whole wall. If you are that satisfied then maybe just seal the bottom of the board with FM330 (though I prefer belt, braces and other measures!) 

 

The floor is solid - cement over tile. I had a good look again and my guess is it's the cutouts for the pipes. This is the sink/dishwasher area which sits just under a new window - triple glazed.

 

18 hours ago, Redbeard said:

So was there plaster on the wall to which the insulation boards were attached, or bare block? If the former, maybe OK (although personally I don't like trapping gypsum plaster in a 'sandwich' on the cold side). If the latter, there may be leakage. My preference is always for a parge coat (lime for me) as an air-tightness layer before insulating.

 

No bare block. Sadly too late to do much about it now.

[garo99]

Having said that the man who did the job commented on the poor state of the brickwork and did a good bit of repairing/sealing before the PIR boards went on.

[garo99]

37 minutes ago, garo99 said:

No bare block. Sadly too late to do much about it now.

 

Actually I just spoke to the builder again - he's here now - he seated the PIR blocks in something (I didn't catch what - insulation foam?) and sealed up all the joins and gaps. he's pretty confident there's no air leaks except in the area under the sink which he agreed was a potential source of an air leak and he just fixed.

[Redbeard]

Well that sounds a bit positive. Is that the floor dpc I see in one pic? If so, take the opportunity to tape the dpc to the plasterboard (ideally it would be to the VCL -foil - behind the plasterboard but you cannot win them all. Gaps can be air-leaks and since (esp. if you are having MVHR) your ideal is to have the house lined with an air-tight 'bag', those junctions are important. When you deal with one plane think of the joints with all the others, and of continuity - insulation and air-tightness. For example is the kitchen single-storey? If not, my future plans would include taking up floorboards as req'd in the room above, sealing (I would use air-tightness primer and air-tightness tape) around the joist ends (potential source of air-leakage) and then insulate from the kitchen below up to the ceiling (or to the underside of the floor if you intend to 'come back to it later'. I suspect you may have missed a trick in that I assume the insulated plasterboard was fixed up to, and touching, the exg ceiling. If I do a GF room my ideal is to cut back the ceiling and run the insulation all the way up to the floor above, with air-tight works as described. (Yes, on the wall with the jsts parallel you might find a tight space (or no space at all) but cross that bridge when you come to it.

 

It's all tedious, but think of the feeling when you know you've cracked it! Good luck.

[garo99]

Thanks. Yes the floor DPC and I will take care of it before the skirting boards go back on. This is an internal wall but as you said gotta think continuity.

 

You are also correct about insulating up to the ceiling. The kitchen is a funny room with part of it single storey and part of it under the bedrooms. I plan to get the kitchen roof sprayed and will look to make the "joins" up to the bedroom more airtight then.