Low carbon retrofit project in ex-council maisonette

[abernabei]

Hi there,

 

we have recently bought a ground-floor maisonette.

 

The property was built mid-60s.

 

The floor is concrete, as far as we can tell it's got about 5-6cm of screen, then it's currently got bitumen adhesive (asbestos-containing), tiles (asbestos-containing), and laminate on top of that.

Walls are 10cm cavity walls (internal softblock, external bricks) filled with some white cotton-like material that I guess is some kind of mineral wool.

On top of that there's dot-and-dabbed plasterboard.

 

We've been looking into modernising the property.

 

We're thinking of installing Kingspan K118 to exterior walls, 37.5mm.

 

For the ground floor, we really wanted to get UFH however I am not sure what options we have:

ceiling height is currently 235, which is already not a lot, so installing 10-15cm of insulation plus all the rest of the flooring on top of it isn't really an option.

 

Removing the screed would give us those 5-6 additional cm, but I have no idea if we can go below that, given it's not a freehold and it's not an independent house.

 

Even removing the screed, that would probably not be enough space to give it the level of insulation everyone on this forums advises to go for.

 

I had a look at the very informative posts on this forum and it seems like solutions like Total-16 or any other retrofit hydronic would just lead to a massive downward thermal loss.

 

What options do we have? Is there any way we can get UFH and keep reasonable ceiling height?

If we keep radiators, what would your advice be regarding floor insulation? Would it make sense to have a 5cm insulation layer?

I suppose that might help, given the T delta with radiators is not as wide as with UFH.

 

For the first floor we're looking at buying radiators with 2.5x recommended BTUs, in preparation for the ASHP.

[SteamyTea]

I think, actually know, that if you fitted UFH with less than 120mm of phenolic insulation, your heating costs would be high.

It is still worth insulting the floor as much as you can, it is a large area of heat losses.

Large radiators, if the layout is suitable, can be run at low temperature. Placing them on internal walls if possible, or you just get the same thermal problems as UFH.

If you are cladding the exterior, have you checked you can do it safely.

What are you doing about airtightness? And the associated ventilation and heat recovery.

[abernabei]

that's actually a very good point you bring...part of the reason why we were installing K118 is to be able to hide the radiator pipes, which are currently everywhere and cannot be hidden without chasing the softblock.

So the assumption is radiators will still be on exterior walls, however there's 10cm insulated cavity and 25mm K118 + plasterboard, so that should be good enough?

 

All radiators are currently under the windows

[billt]

3 hours ago, SteamyTea said:

It is still worth insulting the floor as much as you can, it is a large area of heat losses.

Large radiators, if the layout is suitable, can be run at low temperature. Placing them on internal walls if possible, or you just get the same thermal problems as UFH.

 

I'm all for insulting my floor.

 

I seriously doubt that there will be much heat loss from a radiator mounted on an external wall. There is no direct conductive path to the outside as there is with UFH so the loss will be much lower. If the house is not well insulated it's much better from a comfort POV to put the radiators in the coolest part of the room, which is usually under the window. Reducing temperature gradients improves efficiency as well; you can reduce air temperature if the room has an even temperature.

 

On internal walls is OK if the property is very well insulated, but this one would not seem to be..

 

While UFH is desirable in the right circumstances, it doesn't sound like a good idea in this property.

[abernabei]

57 minutes ago, billt said:

On internal walls is OK if the property is very well insulated, but this one would not seem to be..

It's not too bad on first floor, is it? 10cm insulated cavity and additional K118, it should go below 0.19 U-value as far as Kingspan's technical team advised over the phone (unless I am misremembering), assuming the cavity insulation is mineral wool.

Not a passivhaus. sure

 

57 minutes ago, billt said:

While UFH is desirable in the right circumstances, it doesn't sound like a good idea in this property.

thanks for confirming...disappointing but we'll deal with it.

Any advice on floor insulation that might work for this property, given the restrictions?

 

I have also been wondering, is there any chance this property (maisonette, mid 60s) has DPM?

Could it be they built it with the assumption the bitumen adhesive of the tiles would work as vapour barrier? (if that's the case, we'd have to replace the asbestos-containing bitumen with something else).

5 hours ago, SteamyTea said:

If you are cladding the exterior, have you checked you can do it safely.

What are you doing about airtightness? And the associated ventilation and heat recovery.

 

We are insulating internally with insulated plasterboard, K118.

No plan for airtightness 😅 Happy to look into cost effective measures

 

I found this article which seems to kind of hint at the fact that 25mm XPS insulation *might* be enough to have a reasonable heat loss with UFH?

https://www.homebuilding.co.uk/advice/retrofit-underfloor-heating

 

The "Conclusion" section of https://underfloorheating1.co.uk/blog/article/do-i-need-to-insulate-with-a-retrofit-system also hints at the fact that 25mm XPS insulation *might* be enough to make UFH not a complete waste of money?

Edited October 2, 2023 by abernabei

[abernabei]

any other advice?