External insulation - extend down to foundation level

william

Hi,

We've had a ewi contractor to the house to price for externally insulating the house. He said that there was no benefit in insulating below the level of the footpath as the internal floor level is several inches above.

His logic makes some sense to me. Would anyone have an opinion on this? Would be much appreciated. Some photos attached.

Thanks,

William

delfagio

If I were you and it's an older house with no floor insulation, then I would extend the external insulation down to the footings,
This would prevent the cold bridging between the external wall and sub floor

william

Thanks Delfagio

How far below the path would you think that would be?

William

con1982

There is an advantage to insulating as far as the footings, but it is questionable in a refurb job if it is worth the cost of digging up concrete paths.

Is it a detached, semi or terrace?

william

It's detached Con.

Dudda

I dug out all our footpaths and went down a min of 300mm and probably 500mm on average. It's a large detached 1980 house. I was moving out a lot of the rainwater drainage pipes and downpipes too. It is a lot of work and I calculated the thermal bridge for my house and it was worth it. Cost wise it wasn't huge as we were replacing paving and patio and I dug everything myself. Only a very small extra cost for the insulation going down further.

listermint

Ours has concrete floor slab throughout so I'll definitely be going below level to insulate the slab.

Plan is to cut away the path with consaw and dig down

Doing that myself to remove the labour costs

william

Dudda/Listermint

Thanks for the replies. Really interesting. Also interesting that the depth varied between 300mm and 500mm.

Ours is a suspended ground floor. How do you think one could calculate how deep to run the external insulation? What's the reference point, as in should it be say 500mm below the internal floor level or say 300mm below the bottom of the crawl space (which I presume is earth as it's an old house) under the suspended floor?

Would you have any photos or drawings by any chance?

William

william

One other question. What working space would you think the contractor would need? If the ewi was say 4 inches would it be an additional 6 inches?

And would the base of the ewi need to be sealed to stop moisture travelling upwards behind the insulation?

listermint

william wrote: »

One other question. What working space would you think the contractor would need? If the ewi was say 4 inches would it be an additional 6 inches?

And would the base of the ewi need to be sealed to stop moisture travelling upwards behind the insulation?

Depends on the insulation mine is to be 200mm so plan to have another 100mm in there which will fill with aggregate afterwards.

As for the moisture no the normal damp proof course will protect the brick work as before and the ewi that goes below ground should be spec to be emersed in water.

dathi

william wrote: »

Ours is a suspended ground floor. below the bottom of the crawl space (which I presume is earth as it's an old house) un

how are you insulating your suspended timber floors?

william

dathi wrote: »

how are you insulating your suspended timber floors?

I'm not. It would be a huge job as most floors are tiled over or have parquet flooring put on timbers.

william

listermint wrote: »

Depends on the insulation mine is to be 200mm so plan to have another 100mm in there which will fill with aggregate afterwards.

As for the moisture no the normal damp proof course will protect the brick work as before and the ewi that goes below ground should be spec to be emersed in water.

Thanks. +100mm seems right. Have you selected your above and below ground ewi material?

BryanF

william wrote: »

Dudda/Listermint

Thanks for the replies. Really interesting. Also interesting that the depth varied between 300mm and 500mm.

Ours is a suspended ground floor. How do you think one could calculate how deep to run the external insulation? What's the reference point, as in should it be say 500mm below the internal floor level or say 300mm below the bottom of the crawl space (which I presume is earth as it's an old house) under the suspended floor?

Would you have any photos or drawings by any chance?

William

are you filling in the ground floors with insulation and concrete?

Calahonda52

Dudda wrote: »

I dug out all our footpaths and went down a min of 300mm and probably 500mm on average. It's a large detached 1980 house. I was moving out a lot of the rainwater drainage pipes and downpipes too. It is a lot of work and I calculated the thermal bridge for my house and it was worth it. Cost wise it wasn't huge as we were replacing paving and patio and I dug everything myself. Only a very small extra cost for the insulation going down further.

Looking for some help with the math on the TB here?
Back of envelope sketch attached for discussion: its Sunday so a glass of red or two on board so may be missing something here

Normal EWI is 1 and 2, so the math is about EWI 3

dathi

william wrote: »

I'm not. It would be a huge job as most floors are tiled over or have parquet flooring put on timbers.

well this will become the weakest part of your building . you will still have to keep the floor vents on your external wall to allow ventilation under the floor to remove moisture . if you think about it all you have between you an the outside air is 20mm timber floor board. so you will have cold external air striping heat from the floor boards. also as it is not sealed the cold air leaks into the room.

air

The suspended floors remove a lot of the justification for insulating down to the footings IMO. The wall is going to lose all it's heat from the other side anyway as the space has to be ventilated and thus will be cold.

listermint

air wrote: »

The suspended floors remove a lot of the justification for insulating down to the footings IMO. The wall is going to lose all it's heat from the other side anyway as the space has to be ventilated and thus will be cold.

Sorry but that is not true at all whatsoever.

Just because a floor is suspended doesnt automatically make it more thermally efficient.

air

listermint wrote: »

Sorry but that is not true at all whatsoever.

Just because a floor is suspended doesnt automatically make it more thermally efficient.

That's great because I didn't say anything like that. What thread are you reading exactly?

william

BryanF wrote: »

are you filling in the ground floors with insulation and concrete?

Hi Bryan.

Doing nothing with the ground floor. It's timber boards with 33cm void above earth (I assume). Void has vents to the external.

william

air wrote: »

The suspended floors remove a lot of the justification for insulating down to the footings IMO. The wall is going to lose all it's heat from the other side anyway as the space has to be ventilated and thus will be cold.

Would some form of trickle vent overcome the loss of heat issue?

BryanF

william wrote: »

Hi Bryan.

Doing nothing with the ground floor. It's timber boards with 33cm void above earth (I assume). Void has vents to the external.

Best to do something about floor insulation & air-tightness

air

william wrote: »

Would some form of trickle vent overcome the loss of heat issue?

No, if a space is ventilated to outside it's going to be at the outside air temperature more or less.
IMO insulating down to the footings doesn't make sense unless you insulate the other side of the walls from the crawl space which doesn't sound practical in this case.
I've heard of people fitting insulation crawling through the space under the floor on their backs but it's not a job I'd fancy.

loyatemu

air wrote: »

No, if a space is ventilated to outside it's going to be at the outside air temperature more or less.
IMO insulating down to the footings doesn't make sense unless you insulate the other side of the walls from the crawl space which doesn't sound practical in this case.
I've heard of people fitting insulation crawling through the space under the floor on their backs but it's not a job I'd fancy.

Kingspan (and others) make a product specifically for insulating under suspended floors; but if he's only got 33cm to work with I think that's a non-runner without lifting all the boards. We have nearly 5 feet under our timber floor (dunno why), but I still wouldn't fancy the job.

william

Thanks everyone.

It may be possible to insulate some of the floors in a few years time as part of another project.

From reading the Kingspan brochure (http://www.kingspaninsulation.ie/getattachment/b9b1aa6b-1f43-451c-913c-2a2530c6bff7/Kooltherm-K3-Floorboard.aspx?disposition=attachment) it appears that the external insulation should run 200mm below the floor boards, which in our case should be around ground level. Would you agree with this?

Many thanks,

William

BryanF

william wrote: »

Thanks everyone.

It may be possible to insulate some of the floors in a few years time as part of another project.

From reading the Kingspan brochure (http://www.kingspaninsulation.ie/getattachment/b9b1aa6b-1f43-451c-913c-2a2530c6bff7/Kooltherm-K3-Floorboard.aspx?disposition=attachment) it appears that the external insulation should run 200mm below the floor boards, which in our case should be around ground level. Would you agree with this?

Many thanks,

William

Does that assume that the floor boards and inside of the walls are also insulated?

Given your application I would disagree.

Re not insulating suspended floors, you will regret this next winter.

Dudda

This is a bit like going out with a super insulated big warm jacket and woolly hat in winter but matching it with shorts and flipflops. You've the external insulation and attic done but a very window uninsulated floor.

william

Thanks everyone. We are going to take your advice on board and insulate under the floors. Will look into how to go about this further but one immediate question is what to do with central heating pipe runs which are down in the crawl space?

William

Mercian Pro

william wrote: »

Thanks everyone. We are going to take your advice on board and insulate under the floors. Will look into how to go about this further but one immediate question is what to do with central heating pipe runs which are down in the crawl space?

William

Insulate them well when you have the floor boards up. Also ensure there are no air gaps between the boards after you relay them or between the boards and the skirting.

BryanF

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