Green Building Forum - Retrofit project Wed, 13 May 2026 19:45:12 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Retrofit project https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18435&Focus=310638#Comment_310638 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18435&Focus=310638#Comment_310638 Wed, 13 May 2026 08:29:03 +0100 ChrisGT Cavity walls with 80mm glass wool batts, clod roof, dot and dab plasterboard walls and a terrible airtightness test
Planning to:

Fill cavities below dpc with ecobead.
Create warm roof by increasing rafter depth with intello membrane on inside and blown in gutex or warmcel and solitex plus counterbattens and battens above.

150mm eps from 300mm above ground to foundation fixed to exterior brick walls. Timber frame made from 2 x 50x50mm timber with noggins to create 150mm cavity to be filled with gutex and 40mm rendered woodfibre board outside. Intello against bricks connecting to foundation and roof vapour control layer.

Does this sound like a good plan. Have considered parge coat in wall or passivpurple but intello seems cheaper and more eco.

Triple glazed windows hung outside current wall in picture frame.

Any suggestions or thoughts on improvements?]]> Retrofit project https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18435&Focus=310639#Comment_310639 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18435&Focus=310639#Comment_310639 Wed, 13 May 2026 10:35:59 +0100 fostertom Posted By: ChrisGTTimber frame made from 2 x 50x50mm timber with noggins to create 150mm cavity to be filled with gutex and 40mm rendered woodfibre board outsideWas suggested to me that short (like 1200mm) offcuts of timber I-beam may be available cheap from suppliers, wd save much 'studwork' fabrication on site.
Does the external render-board have to be an expensive insulation board? I thought with thin-web I-beams, thermal bridging doesn't need to be killed?
With I-beams, are 'picture frame' window surrounds needed?
To prevent standing ground-water in the trench, hitting the insulation value of the below-ground CWI and EWI, turn them into french drain? provided you've got somewhere to drain that out to - a soakaway that also fills with groundwater will just pipe water back into the trench.]]> Retrofit project https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18435&Focus=310641#Comment_310641 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18435&Focus=310641#Comment_310641 Wed, 13 May 2026 10:58:33 +0100 djh Posted By: fostertomWas suggested to me that short (like 1200mm) offcuts of timber I-beam may be available cheap from suppliers, wd save much 'studwork' fabrication on site.
Does the external render-board have to be an expensive insulation board? I thought with thin-web I-beams, thermal bridging doesn't need to be killed?
With I-beams, are 'picture frame' window surrounds needed?I'm not sure what you're suggesting to do with the short lengths of I-beam, Tom? I'm not sure there's enough work involved in building the framework Chris suggests to justify trying to save it.

I agree about the outer board - a stronger render board might be better.

The picture frames are needed to box out the light well from outside to inside; otherwise the blown-in insulation will just fill all the space.]]> Retrofit project https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18435&Focus=310645#Comment_310645 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18435&Focus=310645#Comment_310645 Wed, 13 May 2026 13:44:48 +0100 fostertom Posted By: djhnot sure what you're suggesting to do with the short lengths of I-beamScrew em to the brickwork, butting short lengths end to end - dead easy. Just spacers, not doing any spanning.
Posted By: djhThe picture frames are needed to box out the light well from outside to inside; otherwise the blown-in insulation will just fill all the space.
The I-beam spacers can be located to form the sides of the window 'picture frame' - more ditto nogged across top and bottom]]> Retrofit project https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18435&Focus=310646#Comment_310646 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18435&Focus=310646#Comment_310646 Wed, 13 May 2026 16:12:42 +0100 djh Posted By: fostertom
not sure what you're suggesting to do with the short lengths of I-beam
Screw em to the brickwork, butting short lengths end to end - dead easy. Just spacers, not doing any spanning.Sounds more work than building the space frame Chris proposed to me, but each to his own.]]> Retrofit project https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18435&Focus=310647#Comment_310647 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18435&Focus=310647#Comment_310647 Wed, 13 May 2026 17:20:08 +0100 Doubting_Thomas
If the beam isn't structural then it can be just made of a patchwork of different lengths and still work.

Having said that, our carpenter did not enjoy cutting these engineered beams due to the different densities of timber. They were also able to lift each beam into place in one lift, unlike this approach.

So once you factor in the extra cutting, fixing and general labour, I think djh is right - it might not stack up financially, despite potentially being slightly 'greener'.

Worth doing the sums on your particular job though. We had to wait weeks for a special order, so the time factor might swing things.]]>