SIPs house on slope — losing heat through air bricks under floor

[haddock]

Hello,

 

My SIPs house is built on a slight slope, and end of the house where the foundations are exposed there are two air bricks, which I think are losing a lot of heat in today's weather. I'd forgotten they were there but the thermal camera shows them up. When I say foundations, I mean a space about 1.0m high which runs under the floor throughout the house, below SIPs level. It has a layer of thick insulation duvet at the bottom. I've attached a couple of pics.

 

Can anyone more experienced with SIPs construction (or perhaps just construction generally) comment on why these air bricks are there, and whether I could block them up to keep the heat in? One of them is under an open-plan space, but the other under a bedroom and if you leave the bedroom door closed the room never warms up despite receiving the same flow of warm air as other rooms. There could be some other reason for the heat loss but the air brick seems the most likely cause.

 

Thanks for any help!

[Temp]

15 minutes ago, haddock said:

It has a layer of thick insulation duvet at the bottom.

 

Not sure where you mean but there shouldn't be ventilation of the warm side of the insulation. The cold side can be ventilated but not the warm side.

[ProDave]

What exactly is the floor make up, including this duvet you talk about?

 

A timber suspended floor needs ventilation.  But if the floor structure is built properly the heast lost through the floor should be no more and hopefully less than the heat lost through the walls.

 

Did you have it built?  If so do you recall much about the process?  A lot of causes of excessive heat loss are poor detail, like for instance gaps in the insulation or an over large hole where e.g drain pipes exit etc.

[haddock]

20 minutes ago, Temp said:

 

Not sure where you mean but there shouldn't be ventilation of the warm side of the insulation. The cold side can be ventilated but not the warm side.

 

Right! This might be the nub of it. My floor is made of concrete beams; I had to break through one earlier in the year to look into a drain problem and about 1.0m under the beams is the insulation duvet (the drain under that). When you say cold side, that would be another layer of foundation under the duvet?

[ProDave]

Okay so block and beam floor.  What insulation was placed on top of that?

 

Do you have a picture of this insulation duvet?

[haddock]

15 minutes ago, ProDave said:

What exactly is the floor make up, including this duvet you talk about?

 

Did you have it built?  If so do you recall much about the process?  A lot of causes of excessive heat loss are poor detail, like for instance gaps in the insulation or an over large hole where e.g drain pipes exit etc.

 

It was built by the previous owner, whose wife was taken ill during the build and later the construction company went bankrupt. So although it's supposed to be a passivhouse (certification was refused only because the internal garage door isn't up to spec), the thermal performance is not great and there are problems of poor detailing in all aspects of the house that I'm slowly working through

[Temp]

21 minutes ago, haddock said:

 

Right! This might be the nub of it. My floor is made of concrete beams; I had to break through one earlier in the year to look into a drain problem and about 1.0m under the beams is the insulation duvet (the drain under that). When you say cold side, that would be another layer of foundation under the duvet?

 

That sounds odd.  With a beam and block floor the insulation normally goes on top of the beams with a 2-4" screed on top of that insulation. 

 

Is it possible the 1m void under the floor was originally fully filled with some sort of insulation fibre that has got wet and slumped down into a layer that looks like a quilt? I hope not.

 

 

[Temp]

42 minutes ago, haddock said:

When you say cold side, that would be another layer of foundation under the duvet?

 

No it's just a general principle. All walls, floors ceilings etc should have an insulation 8layer in the sandwich somewhere. One side of that insulation is the warm side and the other side is the cold side. As a general rule the warm side shouldn't be ventilated but the cold side can be (in some cases must be). 

 

In most Beam and Block floors the insulation is on top of the Beams and Blocks so the void under them would be on the cold side of the insulation and ventilated.

 

If the insulation is on the floor of the void the space above it is on the warm side and shouldn't be ventilated. However this would be an odd set up. Hence both @ProDave and me would like to know exaxtly what the Beam and Block floor make up is.

Edited November 26, 2023 by Temp

[haddock]

Can't find any pics so just opened up the little hole in the floor I made a few months back. Quite a breeze coming up through the hole but it's not cold. Can confirm there is insulation on top of the beam/block floor (like a Kingspan kind of foam), with 2" screed on top of that. The duvet I'm talking about is much lower down.

[ProDave]

Block up and completely seal the hole you made, otherwise that will be letting heat out.

[saveasteading]

How thick is the floor? 

Presumably there is a 100mm concrete block, filling between beams, then a pir layer above, then the screed.

 

That would not require air bricks in the void, as there isn't timber that would rot.

 

 

I have often toyed with ways to insulate underneath a beam and block floor, but always decided against. 

The duvet thing seems unusual. Perhaps an idea gone wrong. Can you prod it or even hook some out?

It being wet is a concern too. More thought required.

 

Once all done, you will need to find a good way to infill and insulate the inspection hole.

[haddock]

12 minutes ago, saveasteading said:

How thick is the floor? 

Presumably there is a 100mm concrete block, filling between beams, then a pir layer above, then the screed.

 

That would not require air bricks in the void, as there isn't timber that would rot.

 

 

I have often toyed with ways to insulate underneath a beam and block floor, but always decided against. 

The duvet thing seems unusual. Perhaps an idea gone wrong. Can you prod it or even hook some out?

 

 

I now realise I've omitted to mention an important piece of the jigsaw — the house is heated by hot air blown through metal ducts that run deep under the floor, about the level of the duvet. So that could explain the necessity of two insulation layers.

 

Thanks both for emphasising the need to seal the inspection hole, which I will, but the cooling caused by the hole is nothing compared to whatever is cooling the bedroom at the other end of the house where the foundation is exposed.

[saveasteading]

1 hour ago, haddock said:

hot air blown through metal ducts that run deep under the floor, 

Are the ducts insulated?

[haddock]

22 minutes ago, saveasteading said:

Are the ducts insulated?

No way for me to know unfortunately. They’re carrying 60 degree air at 1600m3/h so it’d be surprising if there wasn’t significant heat leaking out either way. 

[haddock]

Thanks again for the comments. I've found an old letter from during the build saying the building guarantee's surveyor insisted on "sub-floor ventilation" against the wishes of the builder and architect. Building control's project manager said "sub-floor venting can be omitted provided precautions have been taken to remove the possibility of organic matter being present" and it says this was done. So I'm going to block up these vents at least temporarily and see what effect it has on my problem.