Low profile insulation retrofit for screeded concrete floor and wall insulation upgrades

[abernabei]

Hi everyone,

 

we're looking at insulating the floor of our ground floor maisonette.

As discussed at

UFH isn't really an option for our property unfortunately, so we're looking at whether we can improve anything before installing new flooring and radiators.

 

Ceiling height is already low-ish (235, might drop to 230cm if we have to go for a second ceiling).

 

Does anyone have advice on low profile insulation boards that might fit our use case?

I was thinking of going for 20mm XPS boards, or maybe Aerogel?

then possibly adhesive and tiles? Or would laminate work better given the low floor insulation?

 

We're also looking at infrared ceiling panels as a heating option for the ground floor, does anyone have any opinion on those?

 

As far as walls are concerned, the current walls are 10cm concrete block, 10cm insulation (white cotton-like material, mineral wool?), then decorative bricks.

The plan there is to install Kingspan K118 insulated plasterboard internally, 37.5mm (25mm 0.019W/mK plus plasterboard).

Is that a sensible plan? or should we consider a different product or a thicker option?

Edited October 4, 2023 by abernabei

[abernabei]

anyone?

[LiamJones]

I’d run the numbers through ubakus.de and the JS Harris spreadsheet https://forum.buildhub.org.uk/applications/core/interface/file/attachment.php?id=18333

 

You can then evaluate payback periods for the different options you’re considering. 
 

FWIW my last place I did I wasn’t aware of this forum and the knowledge it contains. It was solid floor and I just went the with wunda over floor UFH boards. They seemed to work well. I didn’t upgrade insulation anywhere else. My biggest issue was actually draughts and air tightness. 

[JohnMo]

On 04/10/2023 at 00:58, abernabei said:

20mm XPS boards, or maybe Aerogel?

Not sure aerogel would be suitable for the floor, as it's quite fibrous so would compress. 

 

Infrared heating, is still trying to heat the room, is basically 100% efficient, same as any electric heater. Maybe in your shed for a quick hit of heat, but convinced for the house.

 

Basically the more insulation, the better the outcome, but also spend as much or more on draft proofing and then think about your ventilation strategy while your at it.

[abernabei]

13 minutes ago, LiamJones said:

 It was solid floor and I just went the with wunda over floor UFH boards. They seemed to work well. I didn’t upgrade insulation anywhere else. My biggest issue was actually draughts and air tightness. 

 

This is actually very interesting insight as there seems to be consensus that slim UFH boards on top of uninsulated boards will lead to a lot of heat loss and waste of money.

 

Were your bills acceptable even with the retrofit slim UFH? 

 

Yeah, I am aware of the calculator, thanks for pointing it out though

 

I am mostly interested in advice on solutions, as I don't have a U-value target I am aiming for, there are pros and cons for all choices of U-value.

 

6 minutes ago, JohnMo said:

Basically the more insulation, the better the outcome, but also spend as much or more on draft proofing and then think about your ventilation strategy while your at it.

That is true.

I suppose my question is more about trying to understand how bad things will be if we put little or no insulation.

 

Ventilation strategy...none, at the moment any good primer? 

[JohnMo]

20 minutes ago, abernabei said:

Ventilation strategy...none, at the moment any good primer? 

Basically as you reduce leakage, CO2 and mould become an issue. I am a fan of MEV, but only when it's done via humidity control, so the extract points open and close based on the local humidity and so do the inlets either trickle vents or wall vents.  The MEV fan speed automatically changes based on system resistance. So it only ventilates when needed. You inlet to dry rooms and extract from wet. If ducting to wet rooms is an issue dMEV, with humidity boost, but with humidity controlled inlets in dry rooms, not manual.

[saveasteading]

1 hour ago, abernabei said:

how bad things will be if we put little or no insulation.

 

I live in a conversion. We did what was easy, pir boards inserted between the wall studs. Quilt in the attic

The floor is uninsulated concrete, and the heat loss is huge, esp with tiled or board flooring.

If I was doing this now, I would put in whatever thickness the floor finishes could take, allowing for door heights.

If that is 10mm, I would do it as it will be very much better than zero.

That won't look great on a spreadsheet but the reality, allowing for daily heating patterns, will be worthwhile.

And as above, draughts. I'd search them all out and somehow kill whatever I could.

[abernabei]

 

1 hour ago, JohnMo said:

Basically as you reduce leakage, CO2 and mould become an issue.

 

thanks, I'll keep that in mind...is that something we could add-on without too much disruption after works are complete and we have moved in? Or does it require creating ducting in all rooms, lots of dust etc?

 

4 minutes ago, saveasteading said:

 

I live in a conversion. We did what was easy, pir boards inserted between the wall studs. Quilt in the attic

The floor is uninsulated concrete, and the heat loss is huge, esp with tiled or board flooring.

If I was doing this now, I would put in whatever thickness the floor finishes could take, allowing for door heights.

If that is 10mm, I would do it as it will be very much better than zero.

That won't look great on a spreadsheet but the reality, allowing for daily heating patterns, will be worthwhile.

 

Oh, that's very useful to know. It's my gut instinct, too...even though the U value won't be great with 1/2cm of insulation, it might still at least feel a lot better than without any, considering heating patterns etc

Quote

And as above, draughts. I'd search them all out and somehow kill whatever I could.

any tip on that?

I am already planning on building a DIY thermal camera to find cold spots.

Edited October 26, 2023 by abernabei

[saveasteading]

12 minutes ago, abernabei said:

building a DIY thermal camera to find cold spots.

That should do it for cold air coming in, but not hot air going out.

Then smoke sticks or joss sticks at the interfaces.

 

Our original windows were so draughty that it seemed pointless, plus fuel bills are much increased.

[LiamJones]

8 hours ago, abernabei said:

Were your bills acceptable even with the retrofit slim UFH? 

 

In my opinion, yes. It was a 3 bed 1950 semi about 90m2. Filled cavities. Double glazing. Gas combi.

 

Annual space heating demand of approx 8kWh

 

 

[abernabei]

Thanks for that, Liam.

 

At the moment, we are looking at adding "some" insulation on top of the screed.

 

I did some research, it seems like we could add the following on top of the current screed:

- DPM

- 25mm XPS board (Polyfoam XPS?). Could we use PIR too? or is the lower compressivity a deal breaker?

- 18/22mm P5 chiboard (or 18mm plywood like Wisa SpruceFloor)

- 5mm laminate underlay

- 12mm laminate

 

The subfloor could also be done using StyroFloor, I suppose? Would that be preferable even to the plywood option, given the chipboard is already glue to the insulation?

Edited November 4, 2023 by abernabei

[saveasteading]

11 hours ago, abernabei said:

we use PIR too? or is the lower compressivity a deal breaker?

Should be ok as the board will spread the load. You can walk on pir if your feet are kept absolutely flat.

 

Not infra red. It is for corners of garages, patios etc , not for for domestic.

 

Edited November 5, 2023 by saveasteading

[abernabei]

The infrared panels were advice from an architectural techonlogist 😅

 

Thanks for the advice, I suppose by "board" you are referring to the chipboard (which will spread the load).

 

As this will be the main living room, kitchen, dining room area it's the place that will see highest foot traffic, especially during parties etc

[saveasteading]

What about door heights?

 

1 hour ago, abernabei said:

infrared panels were advice from an architectural techonlogist 😅

They're good for heating a person sitting adjacent in a cold space. Otherwise, they are simply electric heaters, and no more efficient.

 

[Mr Punter]

I recently looked at heated skirting and the costs were not ridiculous.  It still needs piping up, like your radiators, but you have more freedom placing furniture.

 

With your floor, if you can get a bit of height by taking up the screed you could then add, say, 50mm PIR and 22m floating chipboard.

[abernabei]

yeah taking up the screen would be ideal...I'm a bit concerned about what's going to happen once we do remove that, assuming we're even allowed...

so for now I think we're only considering proposals on how to insulate on top of the existing screed.

 

P/A is about 0.4

 

I am also a bit unsure whether it could make sense to keep the thermal mass of the current screed+slab rather than going through a lot of disruption to add just a bit of insulation on top of it, partial decreasing thermal mass.

11 hours ago, saveasteading said:

What about door heights?

I am hoping that's not a problem as entrance and patio doors are already at a higher level. The rest of the doors were to be replaced in any case, frames included.

Edited November 5, 2023 by abernabei

[Iceverge]

Dig out the floor. It's a day or two of work. Add 200mm PIR or 300mm EPS, screed or power floated concrete floor. You can use the opportunity to run wiring in conduit to all the outlets and avoid pulling down ceilings. 

 

Otherwise. 

 

PIR as much as you can. 

9 or 11mm OSB in two layers floating over the top, joints crossed, screwed and glued. Cork tiles or carpet. 

 

 

 

 

 

 

[abernabei]

Not sure we're allowed to dig out the slab, it's a maisonette in a council block, there's another maisonette above ours.

 

We're considering removing just the screed or just adding thin insulation on top.

 

What's the rationale behind 2 layers rather than a single 18mm layer, out of interest?

[Iceverge]

1 hour ago, abernabei said:

Not sure we're allowed to dig out the slab, it's a maisonette in a council block, there's another maisonette above ours.

 

We're considering removing just the screed or just adding thin insulation on top.

 

What's the rationale behind 2 layers rather than a single 18mm layer, out of interest?

 

It's highly unlightly the slab is structural. The load from the above flat and the roof will be transmitted to the ground by the walls extending right through to the foundations. 

 

What is the existing floor? You speak of a screed. In all probability it's a concrete floor. Probably about 100mm thick. 

 

 

Insulation is plenty strong enough to take distributed loads. You can put a whole house on it in the case of an insulated raft foundation. However it doesn't like point loads, think high heals. 

 

If you had only one layer the risk is that at the joint the OSB/PLYWOOD wouldn't be able to distribute the load sufficiently and would sink into the insulation making a wonky floor. 

 

 

[abernabei]

The builder dug a bit of it and said it's a 5-6cm screed as it was quite "soft" (it was just a quick test so we're not sure about depth), compared to concrete.

21 hours ago, Iceverge said:

If you had only one layer the risk is that at the joint the OSB/PLYWOOD wouldn't be able to distribute the load sufficiently and would sink into the insulation making a wonky floor.

I see, I would have thought 18mm T&G would be able to handle that scenario. Thanks for the clarification

[saveasteading]

8 minutes ago, abernabei said:

18mm T&G would be able to handle that scenario. Thanks 

One sheet, however thick, has a flexibility at the junctions. Thus 2 staggered  sheets of 9mm provide a more complete and even and stiff surface than 1 of 18mm.

[abernabei]

Glued T&G, I meant

it is also true that a single 18mm layer should be stiffer (in the central part) than 2 9mm though, right?

 

I see what you mean though, even if glued the junctions will be a weak point 👍

[abernabei]

Hi everyone, updates:

 

Concrete ground floor insulation:

we dug the screed out a bit here and there. As it turns out, the concrete slab on the ground floor, just like on the first floor, is very uneven.

 

The screed is about 2.5cm thick at the sides, and 5.5-6cm in the middle of the room.

That means we would have had to have the asbestos bitumen adhesive ground, then dig out the screed and fill in partially again to make it level before adding insulation.

All of that for just a bit more than 2cm of extra height compared to not digging it.

 

For that reason, we have decided to leave the current screed as it is.

 

We are covering it with a "dpm sandwich"

- Mapei Latexplan Trade Fast (the "Fast" is an important detail as its composition is like their "No Ammonia" latexplan, i.e. t sticks to bitumen, unlike standard compounds like their Ultraplan 3240 or the standard Latexplan Trade). Moreover, this has much compressive strength than Latexplan No Ammonia. This allows us to do the top coat of the dpm sandwich using Ultraplan 3240, which has a lower compressive strength than Trade Fast and is much cheaper than No Ammonia, which is what we would have had to use as top coat had we used No Ammonia in this first layer too.

- Mapei Mapeproof One Coat

- Mapei Grip T Plus primer

- Mapei Ultraplan 3240

 

I am posting all these details hoping they are useful to someone else in the future, as this was all approved and recommended by Mapei's technical support

(indeed, the idea to use Trade Fast to allow using Ultraplan 3240 on the top coat was their recommendation)

 

On top of that, I'd like to add some insulation but without losing floor height.

 

Question: what do you think about using

- insulated cement boards, like 20mm XPS with 0.5mm glass-fibre mesh reinforced  polymer-modified cement mortar.

or

- XPS 400-500kPa

or

- EPS 400kPa

 

and then install the underlay and laminate straight on top of it?

Would it work, given the high(er) compressive strength?

 

Or do we really need to lose another 18/22mm for chipboard/plywood?

 

There is no floor height for having that extra layer of chipboard/plywood, so if 400-500kPa boards are not enough by themselves, I think I'll have to let go of insulation

 

 

[abernabei]

Regarding cavity wall insulation:

as it turns out, what we believe was sagged wool insulation turned out to be just a sloppy job.

Ground floor walls are still mostly full and not moist, first floor is mostly empty.

They basically did not the first floor at all.

The company who attended said maybe it was done as part of a government funded initiative to insulated council blocks and so the installers had way too many jobs to do in a day to care about insulating it properly.

 

A few companies came over to do a survey and provide a quote.

 

Ultimately, I think we'll be going for wool.

 

I hear a lot of good things about bonded beads, but lots of installers complained about the problems in getting the right amount of glue out of the nozzles.

They say they easily clog and it's hard, as an installer, to know when they stop working.

 

They said you need to manually check whether the glue is still flowing, and when it's not, you can't be sure how long exactly you're been blowing beads without glue...

 

That in itself seems a deal breaker to me.

 

Considering the property was already (albeit poorly) insulated with wool and it didn't really sag and it doesn't seem moist, I think going for wool might make more sense.

The reason behind that is that if anything goes wrong and the installer does not want to accept responsibility (something that seems to be happening more often than not), beads will be a lot more expensive to extract.

 

What do you think?

 

@JohnMoregarding ventilation: I am catching up on the topic. The current plan is use a MEV for utility and toilet room plus a dMEV in the kitchen area (as well as a ceiling hood), which is not conveniently located to be ducted to the MEV.

What do you think? Any recommendations for brands/models?

[abernabei]

I forgot to mention that the laminate would be 12mm, so fairly rigid.

I could also consider engineered wood, if that meant not needing the plywood/osb/chipboard subfloor