Green Building Forum - Insulate cavity during wall repair and blocking up windows Wed, 10 Jun 2026 10:58:17 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Insulate cavity during wall repair and blocking up windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17899&Focus=302438#Comment_302438 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17899&Focus=302438#Comment_302438 Thu, 13 Jul 2023 19:12:20 +0100 GreenApprentice
W’ve now removed the boiler and I’m repairing the botched wall that was glued back together with expanding foam. All the loose fibre insulation in the area has left the building when they knocked the more than foot square hole through to fit the tiny flue.

I’ve bricked up the outside and now wondering how best to insulate the cavity - we are doing EWI, but with what I’ve read, feel we should fill the cavity.

The complication is that the adjacent wall looks to also have lost its insulation above this level. It has a window that will be blocked up at some point in the near future and that will also need the same consideration, so using loose stuff now will probably be pointless.

Also, we have some windows and a door to block up and our wall builder guy has said to use thermalite blocks on the inside of cavity and solid blocks for the outside skin with ‘wall log’ in between. Is this ok or can we better it and could I use this ‘wall log’ or alternative in the boiler hole repair?

Thanks in advance,
Denys]]> Insulate cavity during wall repair and blocking up windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17899&Focus=302440#Comment_302440 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17899&Focus=302440#Comment_302440 Thu, 13 Jul 2023 20:02:55 +0100 djh Insulate cavity during wall repair and blocking up windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17899&Focus=302444#Comment_302444 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17899&Focus=302444#Comment_302444 Thu, 13 Jul 2023 20:42:36 +0100 GreenApprentice Posted By: djhWhat is ‘wall log’?
I think he’s referring to fibre type insulation that’s specifically for putting in the cavity during wall construction. I did Google wall log insulation and I just get loads of websites talking about insulating log cabins.

Any advice on what the best thing to buy for the job would be appreciated.]]> Insulate cavity during wall repair and blocking up windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17899&Focus=302446#Comment_302446 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17899&Focus=302446#Comment_302446 Thu, 13 Jul 2023 20:46:08 +0100 philedge Insulate cavity during wall repair and blocking up windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17899&Focus=302452#Comment_302452 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17899&Focus=302452#Comment_302452 Fri, 14 Jul 2023 09:11:38 +0100 Dominic Cooney Insulate cavity during wall repair and blocking up windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17899&Focus=302453#Comment_302453 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17899&Focus=302453#Comment_302453 Fri, 14 Jul 2023 09:22:39 +0100 GreenApprentice Posted By: Dominic CooneyDoes the wall guy know that you are going to EWi?
Yes

Posted By: Dominic CooneyCome to think of it, how thick will the EWI be? 200? 300? Some advocate filling the cavity with concrete if all the insulation is on the outside.


150mm]]> Insulate cavity during wall repair and blocking up windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17899&Focus=302673#Comment_302673 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17899&Focus=302673#Comment_302673 Mon, 31 Jul 2023 20:44:38 +0100 GreenApprentice
There is a large wood lintel inside and a steel angle iron outside supporting the bricks over the window - we are planning to leave these in place, blocking up to them, to make the window half the size it currently is.

We’re going to open the cavity and use isover 36 100mm cavity insulation in the 100mm cavity (we have loose fill fibre cavity insulation that I am planning on keeping in place with this stuff as we remove the bridging masonry)

We’ll block up half the window opening with 100mm solid concrete block on both skins and full fill the cavity. Should we remove the vertical DPM that is there or leave it and same for horizontal DPM that sits under the steel?

Should we be adding a new DPM to the new window reveal created? - We’re planning on replacing the remaining half of the window soon (it’s two windows fastened together currently) but placing it outside the outer wall so it sits in the EWI - currently researching the materials to do this properly. I saw a video that mentioned that vertical DPM around a window may be a problem for moving the window out. Not sure what to do to make this not a problem. Any ideas also welcomed.]]> Insulate cavity during wall repair and blocking up windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17899&Focus=302674#Comment_302674 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17899&Focus=302674#Comment_302674 Mon, 31 Jul 2023 20:51:13 +0100 GreenApprentice Insulate cavity during wall repair and blocking up windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17899&Focus=302675#Comment_302675 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17899&Focus=302675#Comment_302675 Mon, 31 Jul 2023 20:52:44 +0100 GreenApprentice Insulate cavity during wall repair and blocking up windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17899&Focus=302677#Comment_302677 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17899&Focus=302677#Comment_302677 Mon, 31 Jul 2023 23:05:58 +0100 tony
EWI plan sounds OK, the more insulation value that you can get the better.

I agree dense blocks for the outside skin

I would go medium density for inside skin.

While you are in this mess how about removing the window board and the reveal to the other half of the window and doing cavity insulation properly, removing any thermal bridging.

Wet plastering is best for internal finish

Check wall insulation joins seamlessly with loft insulation.

Nice job!]]> Insulate cavity during wall repair and blocking up windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17899&Focus=302678#Comment_302678 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17899&Focus=302678#Comment_302678 Mon, 31 Jul 2023 23:58:51 +0100 GreenApprentice Posted By: tonyWhere the window will be removed you can remove the vertical dpc.

EWI plan sounds OK, the more insulation value that you can get the better.

I agree dense blocks for the outside skin

I would go medium density for inside skin.

While you are in this mess how about removing the window board and the reveal to the other half of the window and doing cavity insulation properly, removing any thermal bridging.

Wet plastering is best for internal finish

Check wall insulation joins seamlessly with loft insulation.

Nice job!

Thanks, we’re doing 150mm EWI and have decided to take off fascia’s etc so we can join to new loft insulation - full plan TBC as per what we find when we strip back.

Yes, we were planning to strip back the reveals, saw a video today that suggested that but mentioned there may be a structural element - to be honest, we’re shocked at how poor the walls/window opening has been done, so I think we can only improve it!

Cheers for comments :bigsmile:]]> Insulate cavity during wall repair and blocking up windows https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17899&Focus=302679#Comment_302679 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17899&Focus=302679#Comment_302679 Tue, 01 Aug 2023 07:50:03 +0100 tony