Internal solid brick wall insulation. Insulated plasterboard or what?

[howplum]

My modest 3 bedroom detached house, which is in a conservation area, was built in 1936 and three of the walls are solid, although strangely the south facing wall is of cavity construction, which is insulated.

 

There is a modern composite front door, with a glazed porch, and all the double glazed window panels have been upgraded to the latest specification because the existing 20 year old units were deteriorating.

 

In my view energy prices will ever only get more expensive so I am investigating improving the insulation of the house as whole and think that insulated plasterboard might be the best solution because it seems to give the best improvement without encroaching too much on the floor and being reasonably DIY friendly.

 

Payback is not a factor because the aim is to make the house more efficient in terms of heat retention overall, hopefully with a small reduction in the monthly fuel bill.

 

Apparently, according to Homebuilding.co.uk anyway, the current U-value of a solid brick wall is around 1.9W/m². I have been looking at insulated plasterboard and 50mm Gyproc Thermaline Super allegedly has a U-value of 0.020W/mK - a significant improvement. However, I notice the two figures are expressed slightly differently, is this important? In other words, am I comparing like with like?

 

Does the lower figure of the insulated board override the higher figure of the wall, or is there some formula to combine the two?

 

I appreciate there are practical hurdles to overcome, such as fitted wardrobes, radiators, electrical sockets, window reveals and boards, bay windows, skirting boards, coving, carpets, plastering, decorating and no doubt others I haven't spotted yet. 

 

Obviously this will involve major disruption so I plan to do it on a room by room basis.

 

Any advice, hints or tips would be appreciated.

[George]

No the figures are not directly comparable.

 

Each wall material will have a thermal conductivity (W/mK). The thermal conductivity is multiplied by the thickness and the inverse all of the thermal conductivity x thickness of the wall materials gives the U-value. 

 

A simple to use calculator is by Kingspan, but this is limited to their products. Gives you a good idea, though

 

https://www.uvalue-calculator.co.uk/calculator/

 

 

[howplum]

Thanks George,

 

I had a look at that site, and others, but they don't seem to include solid walls, presumably because they are mainly intended for new builds and extensions. Perhaps the best option is to ask the manufacturer what U-value can be expected.

 

I would still appreciate experiences from anyone who has been down this route though. 

[A_L]

1 hour ago, howplum said:

I notice the two figures are expressed slightly differently, is this important? In other words, am I comparing like with like?

 

They are two different parameters. The second is the thermal conductivity of a single material and is independent of material thickness. A two brick solid wall has a U-value of approximately 2.03. This means it has a thermal resistance of 1/2.03 or 0.49m²K/W Where you have a thermal conductivity the thermal resistance of  a layer is thickness in metres/thermal conductivity. You can then add all the thermal resistances together and take the reciprocal to get the new U-value. 

 

75mm of your insulation will be needed to get below the requirement for renovations to achieve not more than U=0.3 (Part L1B) It will give U=0.234.

[IanR]

2 hours ago, howplum said:

the current U-value of a solid brick wall is around 1.9W/m².

 

50mm Gyproc Thermaline Super allegedly has a U-value of 0.020W/mK 

There is a bit of a mix up in the units.

 

Typical units for U Value are W/m².K . the 1.9 figure you have looks "about right" for a 9" solid wall with some plasterboard on it, so that's probably 1.9W/m².K

 

The value you have for the Gyproc Thermaline Super looks more like a λ (lambda) value ie. Thermal Conductivity of the phenolic foam part of the composite board. The typical units for an λ value are W/m.K.

 

But the boards are made up of gyproc wall board (λ 0.19W/mK) + the phenolic foam (λ 0.020W/mK).

If you wanted to workout the thermal resistance (R value) of the whole board thickness, you need to divide each material's thickness in meters, by its λ value to get its R value, and add the R values together. Typical units for R are m².K/W

For the 50mm thick Gyproc Thermaline then, that's (0.012 / 0.19) + (0.038 / 0.020 ) = 1.96   m².K/W   (I've assumed 12mm gyproc and therefore 38mm phenolic foam)

To get to the U value, you need to 1 / (sum of the R values). For the Thermaline on it's own that means the U vlaue is 1/1.96 = 0.51 W/m².K

 

But to see how this effects your wall if added on, then you need to revert the wall's U value to it's R value ie. 1/1.9 = 0.53 W/m².K

 

And then to get the total U Value of the new wall build up: 1 / ( R of original wall + R of the Thermaline), so 1/ (0.51 + 0.53) = 0.96W/m².K

Edited to add:

There are online calculators to make this easier https://www.ubakus.com/

Edited September 27, 2021 by IanR

[IanR]

12 hours ago, IanR said:

And then to get the total U Value of the new wall build up: 1 / ( R of original wall + R of the Thermaline), so 1/ (0.51 + 0.53) = 0.96W/m².K

Apologies, in the very last calc., I've incorrectly used the the Thermaline's U Value and not its R Value. So, what I should have said is:

 

And then to get the total U Value of the new wall build up: 1 / ( R of original wall + R of the Thermaline), so 1/ (0.51 + 1.96) = 0.405W/m².K

 

Edited to add:

 

...and Ubakus roughly agrees

 

Edited September 28, 2021 by IanR

[howplum]

Thank you all for your responses. I will need to sit down with a cup of coffee and try to understand, although first impressions are that if I go with an insulated board  of 72.5mm (60 + 12.5) then the U-value will be better still. Having had a quick look at Kingspan''s Kooltherm K118 on Insulation Express's website it looks as though the thicker the insulation the cheaper the board! Also, in the grand scheme of things, I suspect a board that is 20mm or so thicker isn't going to affect usability of the room to any noticeable degree.

 

The bay windows, which I suspect might be single brick, will obviously need special consideration, and this article seems to cover it pretty well:

 

https://www.wartonwoodworks.com/how-to-insulate-a-bay-window-warton-woodworks/

 

[howplum]

After a bit of digging it looks as though using a 60/12.5mm insulated plasterboard fixed with dot and dab could reduce the U-Value to around 0.30 W/m²K, which is a lot better than the existing figure.

 

As part of the process I would block up both fireplaces in the lounge/study, which will no doubt help even further.

 

Has anyone out there done this before? It's all very well me reading about it, but there is nothing like a first hand account to bring a sense of reality.

 

 

[A_L]

@howplum, I get U=0.28, given central England and a typical heating regime this will reduce heat loss by about 40kWh/m²/year

[howplum]

Thanks @A_L. I used this calculator https://www.resurgence.org/resources/heac.html and it came up with a cost saving of nearly £500 p. a., albeit based on a unit cost of 5p per kWh, which is higher than my current tariff of 3.4p. Nevertheless, as the years roll by I suspect the job will seem like money well spent by improving the overall efficiency of the house in terms of heat loss.

[howplum]

On the other hand, Spacetherm with aerogel technology offers a number of options worth considering. For example, Spacetherm Wall Liner allegedly offers a 61% reduction in heat loss for solid walls from a thickness of only 13mm, which seems impressive, at least to this layman. One advantage, at least for me, is that the 1200mm x 600mm panels only weight about 3.5kg, which would be especially useful for lining the walls inside the built in wardrobes.

 

There is also Spacetherm Multi for Walls, which offers good insulation options in sheets of various dimensions. However, having to mount them on 25mm battens rather negates their space saving advantage.

 

Has anyone tried the Spacetherm products?

 

https://www.proctorgroup.com/products/spacetherm