Concrete floor insulation retrofit - cold floor

[Nickfromwales]

13 hours ago, gambo said:

There is PB inside but I would be surprised if it was 2 layers or FR.

So, is there any for-dummies description how such conversions should be done?

I get that fire resistance is important so that's something I would rectify. What about floor? If it's just concrete on top of concrete shall I try to skim it and/or put VIP insulation +6mm cement board/plywood + engineered wood?

What can LA say if I go for retrospective permission given it's 30yo?

VIP would bankrupt you. Most expensive and not practical here at all. Likely 10mm of XPS would suffice as a break between concrete and finished floor covering.

 

13 hours ago, JohnMo said:

Think you have two options 

1. Rip it all out and do it correctly - may not be easy unlikely to be cheap. Could grow arms and legs, from a planning perspective and construction scope.

2. Do a good thermal underlay and  good carpet. Pretty cheap, a warmer feeling to the floor, very constrained work scope. If you are concerned with damp, you could do a liquid DPM, which is basically epoxy paint, paint one day underlay and carpet the next.

 

Option 2 and move on with my life, would get my vote. 

 

In a nutshell, what he said.
 

Why fit a floor that creates a problem? Go for wood effect LVT or carpet, and reduce the cost and pain.

 

Or do as you say, and insulate more, say 15 or 20mm in an XPS backer (insulation) board and a thinner engineered floor, and lose some head height.

 

FR PB needs to be to the garage interior so fire is co rained within that ‘cell’. As the walls are breeze block you only need to cover that steel lintel and the 100mm under it, so basically a ribbon of 2 layers of FR PB like a coving, and then the 2 layers on the ceiling, all junctions / joints need to be filled / covered with intumescent caulk.

 

Check the head of any door opening to see if that has the same exposed underside of a lintel, and that the cavities have been closed. Same around the garage door opening. Yes, these are a pita to do, but that’s what building control would ask for / expect to see.

 

It’ll be good if the habitable side of the garage has had a concrete on concrete raised floor, as that will constitute the bund for flammable liquids, again required regardless of what you say you’ll store as it is possible TO store a vehicle / ride on mower etc which is enough to provoke that requirement.

 

The guide would be what your building control officer / architect would put together for you exact circumstances, but the FR(PB etc) / smoke&heat / bund being put in place will allow you to sleep better I guess.

 

We can’t really advise you to look the other way, so if you ask you’ll be told and then you can decide for yourself .

[saveasteading]

Good advice above. I have a feeling that Marmox board is better insulating in a thin board, and I remember it being nicely robust to work with. 

 

I received it on the highest authority that plasterboard joints don't need intumescent filler , but that may not be the understanding among lesser experts.

 

 

 

[Nickfromwales]

58 minutes ago, saveasteading said:

Good advice above. I have a feeling that Marmox board is better insulating in a thin board, and I remember it being nicely robust to work with. 

 

I received it on the highest authority that plasterboard joints don't need intumescent filler , but that may not be the understanding among lesser experts.

 

 

 

The only caveat with XPS / other Marmox type board is point load, so these are usually no good with LVT or carpet, but possibly LVT composite will work. 
 

Intumescent caulk was required by every BCO on each GC I ever did, where the boards were NOT plastered / skimmed. If double layer or skimming, then not required. (AFAIK ). 

[gambo]

Why is VIP not practical? I have one quote for retrofit and it's £8k. So VIP would be just 1-2k and no mess.

I may go for thin engineered wood or LVT but need to do the math on U values.

[Nickfromwales]

2 minutes ago, gambo said:

Why is VIP not practical? I have one quote for retrofit and it's £8k. So VIP would be just 1-2k and no mess.

I may go for thin engineered wood or LVT but need to do the math on U values.

Most would consider that to be expensive, that’s all, when a cheaper option is available.

 

I am unsure of their ability to accept point loads, and whether they’d be easily damaged during installation / service.

 

They’re a bit fragile, and if they are ordered encapsulated then you can’t cut / shape them. 

 

 

 

The greatest challenge to using VIP is that if the vacuum is broken, then the additional lambda value provided by the vacuum is lost. If the vacuum is lost in a VIP panel the resultant Lambda value can increase to around 0.02W/mK, similar to PIR. It is therefore imperative to avoid VIP damage.

Conventional VIPs which are provided without protection can be vulnerable to puncture during handling and installation, needing extra protection layers, with material and cost implications. Installers need to be trained to know not to cut, drill or nail into VIPs and how to handle them correctly.

However, there is a solution to this problem. The best way to ensure the high insulation value VIPs offer is retained, is to ensure they have been fully encapsulated and protected at manufacturing stage, thus reducing the risk of puncture during installation and use.

With the right choice of VIP manufacturer this protection can be provided without losing thermal performance.

[RobLe]

The below U-Vacua works out around £75/m2 from digikey - I think they’re expecting to sell to fridge freezer type applications rather than construction tbh.  Centre panel lambda =0.002W/mK, 10x better than PUR, the one linked is just 15mm thick.  I guess need to be super careful about construction, to make sure it doesn’t and can’t get punctured.
 

https://www.digikey.co.uk/en/products/detail/panasonic-industrial-devices-fbd/cnrzzb98400/9558509

[Nickfromwales]

18 weeks lead time for manufacturing…..

[SteamyTea]

On 09/05/2025 at 16:56, Nickfromwales said:

18 weeks lead time for manufacturing…..

Similar to the early failure rate then.

VIP are not really a product for buildings.

[Nickfromwales]

Just now, SteamyTea said:

Similar to the early failure rate then.

VIP are not really a product for buildings.

Yup. Hence me saying that they’re impractical for this instance 😉

[gambo]

That's what I was worried about. Lots of YTs and articles are from 5-10years ago, perhaps they tried to enter the market and it failed.

[gambo]

Just a random thought, could it be that there is no insulation in my concrete in either of rooms (late 80s house) but the reason it feels cold in the garage conversion is due to cold bridging from either the other garage or driveway?

[gambo]

That's a photo of bricks under window of the garage conversion

[SteamyTea]

14 hours ago, gambo said:

Just a random thought, could it be that there is no insulation in my concrete in either of rooms (late 80s house)

A good thought.

This is how insulation has changed over the decades.