Insulation/Plastering for concrete blocks solid walls

[CarolineTheChemist]

We have an 17th Century timber framed house, with a 2 storey extension added in 1946. It's also grade II listed. We've been doing some work on it recently and have discovered that the extension is built from concrete blocks (some of which appear to be resting on the old timber frame :shock: ) and these have been plastered with what looks like a gypsum based plaster. The outside of the walls are tile hung. The bedroom in the extension is triple aspect and is currently very cold. The walls are very cold to the touch but it doesn't look or smell damp. In the summer it was ridiculously hot as the room gets pounded by sunshine all day. It currently doesn't have any central heating; there is an old fireplace but it is blocked up.

We're quite au-fait with how to insulate and plaster the timber framed parts of the house, but I'm at a loss for the best way to approach the concrete block extension!!

Does anyone have any advice/experience with insulating/heating a room with concrete block solid walls. Especially things you've tried that were a waste of time? I'm considering removing all the plaster and replasting in lime in the hope it is somehow more temperate, but I'm concerned this could end up being a total waste of money! Perhaps it would be good enough if we reinstated the fireplace, installed radiators and just used a fan when it's hot in the summer. Our roofer suggested putting TLX Gold insulation under the external tile hanging... then there's the option of installing internal insulation batts. So many options?!?!?!?!

 

[george2019]

An external insulation system with the tiles rehung as cladding would be my suggestion.

The Kingspan u-value calculator has that exact build up available solid block-insulation-battens/tiles (https://www.uvalue-calculator.co.uk/calculator/), although cheaper manufacturers are available. LBC would be needed but should straightforward if the same tiles/external appearance will be maintained.


I wouldn't worry about gypsum plaster if damp hasn't been an issue. Vapour permeability/wet walls isn't the cause of the cold here, it's the low u-value.

 

[paulc]

Our roofer suggested putting TLX Gold insulation under the external tile hanging...

I've recently been insulating a small room (solid brick walls), and had initially looked at Superquilt (another multifoil insulation). There was no way I could achieve the required level of insulation using Superquilt on its own - The manufacturers specify a layer of the foil sandwiched between battens and topped off with 80mm of Celotex. The layer of Celotex would be sufficient to meet building regs on its own, so no point in using the foil !

Looking at the specs for TLX Gold, it is pretty much the same as the YBS Superquilt (quoted u value of 0.85 m²K/W) - Putting the data through a u-value calculator shows that it will make precious little difference to the thermal efficiency of the wall. This guy did some tests & comparisons which is well worth a read before you waste any money: http://multifoilexperiment.blogspot.com/2006/06/comparison-of-multifoil-insulation-vs.html

I would have suggested Celotex (or similar) to insulate the concrete walls, but not over the timber. The latter needs something breathable and/or some way for moisture or run the risk of rot setting in. Perhaps Celotex over the concrete and cork or wood fibre boards for the timbers would work.

 

[CarolineTheChemist]

Thanks guys! That's reassuring to know that we needn't have breathable insulation for the concrete part.