See the sketch. I have the end of an external wall running into the internal area alongside a window.

I am wondering what level of insulation to use across the end of the spur of external wall (where the external wall was cut back to create an opening).

I can use some insulated plasterboard on the inside of the window reveal, but the end of the spur will be plastered over (wet plaster) with the adjacent brick wall. I guess I need a little bit of insulation between it and the plastering to avoid a possible cold spot in a utility room.

 

Suggestions ?

Thin piece of PIR ?

Something I could spray it with ?

Aerogel matting ?

 

Should I use this stuff ?

 

https://www.insulationuk.co.uk/products/tekwarm-reveal-board-high-performance-laminate?variant=43387649261749&utm_medium=cpc&utm_source=google&utm_campaign=*Pmax|Ins.Plasterboard30+&gad_source=1&gbraid=0AAAAAoNNCLQ_tq0b6Prkw491vqllba1g2&gclid=EAIaIQobChMI7_mygKjujAMVrpFQBh2LXgvDEAQYASABEgJc7_D_BwE

Any advice on this and on boarding reveals generally ?

 

Is this reveal board with 6mm plasterboard and 14mm XPS worth using ?

I am also wondering about how to put fixings into the reveal - for example I will want to put roller blinds in the reveal but they will be positioned alongside the insulated cavity, so how am I going to be able to screw them up ? Do I need to fix some wood or metal in place behind the reveal board that I can fix into ?

 

Is it better to use a tile backer insulated board and is that then easy to fix into ?

Put some PIR in the gap. Then plaster board and plaster. If you want you could use the insulated board instead of plaster board, but then you'd be looking to run it all way along that L shaped wall at the top to maintain the same thickness (and a flat surface to plaster on). Might get expensive.

 

You could use that insulated board for the reveals as well, if there's room.

 

Good rawlplugs (or similar) will hold a roller blind. Usually you have the option to screw the brackets to the top reveal or the side reveals

Edited July 1, 20251 yr by BotusBuild

I can see two problems.

Energy loss 

Condensation risk

 

Energy loss could be counteracted by improving another element i.e. improve the window.

 

Condensation risk is a lot harder and would need some more information.

What is the wall NSEW orientation. South facing would probably not be an issue, North almost certainly is.

You only need a relatively small amount of insulation, maybe 50mm, to stop the wall from dropping below the dewpoint temperature.

You should be able to model that section fairly easily in 1 dimension to get an idea of the scale of the problem.

Failing that, just fully fill the cavity with insulation, but be wary of any existing cavity ventilation already there n place, even if it is already obscured.

20 hours ago, Spinny said:

Is it better to use a tile backer insulated board and is that then easy to fix into ?

Yup, defo.

 

Use Marmox or other no-name XPS boards which will give you an excellent thermal break, and you can plaster straight onto them too. Use the ones with the gritted dark surface vs raw XPS.

 

Same for window/door reveals 👍

On 02/07/2025 at 16:45, Nickfromwales said:

Use Marmox or other no-name XPS boards which will give you an excellent thermal break, and you can plaster straight onto them too. Use the ones with the gritted dark surface vs raw XPS.

@Nickfromwales

Would that include WEDI board like this ... https://www.wedi.net/uk/products/building-systems/building-board/wedi-building-board/      ?

 

This appears to be blue but says it is XPS.

Edited July 8, 20251 yr by Spinny