Wed, 22 Apr 2026 10:31:18 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14646&Focus=248768#Comment_248768 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14646&Focus=248768#Comment_248768 Mon, 24 Oct 2016 22:18:35 +0100 discotroll
I'm just working on the build-up of the proposed insulation and internal structure of a conversion project but I don't seem to be able to find anywhere a clear and definitive guide on what u-values I need to be hitting re floor, walls and roof.

I've read that as a conversion I need to adhere to Doc L1b (something around 0.18w/m2k for the flat roof, etc) then I see that if it's a new roof I need to adhere to new-build targets. I've seen info saying that the u-value can end up worse than a specified target figure and I've read other stuff saying that the overall property needs to come in at a crazy 0.13w/m2k..

I've got my calculator for working out the build-up and thickness of insulation and other materials, but I could do with just knowing that the u-value figure I'm aiming for is 'X' and that is what I must hit to get building regs approval.

If anyone could shed any light on this and how I can move forwards that would be great.

Thanks,

DT.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14646&Focus=248769#Comment_248769 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14646&Focus=248769#Comment_248769 Mon, 24 Oct 2016 22:40:37 +0100 tony
How about aiming at 0.1 and 0.7 for windows.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14646&Focus=248785#Comment_248785 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14646&Focus=248785#Comment_248785 Tue, 25 Oct 2016 11:08:21 +0100 fostertom
So how thick - as you say, what U value? Well, that's what the Passive House approach is about - to define the optimum U value that's sufficient but no more (diminishing returns). That depends on factors particular to each building - local climate, and building shape (i.e. ratio of heat-losing external surface area to useful floor area) mainly. But it'll certainly be higher than 'Bldg Regs', up in the 'crazy' 0.13 bracket.

The optimum is effectively the threshold, the point at which suddenly you don't need to spend money on a heating system, the point at which the building pretty much heats itself unaided, thro solar gain, body and cooking heat etc.

Of course there's more to it than that - airtightness as well as insulation, and 24/7 heat recovery ventilation.

On a conversion (rather than new build) you may not be able to quite get to that optimum overall - the Passive House Enerphit standard shifts its emphases to acknowledge that.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14646&Focus=248791#Comment_248791 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14646&Focus=248791#Comment_248791 Tue, 25 Oct 2016 12:55:48 +0100 ringi https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14646&Focus=248792#Comment_248792 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14646&Focus=248792#Comment_248792 Tue, 25 Oct 2016 12:55:57 +0100 DarylP A 'conversion - change of use' dwelling should meet the minimum stds in AD L1B
https://www.gov.uk/government/publications/conservation-of-fuel-and-power-approved-document-l
However as said above, these are minimum stds... in a few years you will be kicking yourself for not doing it better!
Also the 'Regs' are different in England and Wales.....
Aim for 0.1 U-values across the board, and 1.0 for windows/doors....]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14646&Focus=248804#Comment_248804 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14646&Focus=248804#Comment_248804 Tue, 25 Oct 2016 13:37:01 +0100 JSC
http://www.kingspaninsulation.co.uk/Knowledge-Base/Building-Regulations.aspx

What ringi said is very pertinent.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14646&Focus=248833#Comment_248833 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14646&Focus=248833#Comment_248833 Tue, 25 Oct 2016 18:52:26 +0100 neilu
Starting on page 12, paragraph 4.11 will confirm that a conversion is classed as a material change of use.
The following sections then guide you as to the U-values you will need to achieve.

Any existing retained thermal elements (floors, walls, roofs) need to comply with paragraph 5.12 and table 3. This basically says that if an existing element doesn't achieve a certain U-value then it has to be upgraded. For example an un-insulated cavity wall needs to be upgraded to achieve a U-value of 0.55 which is roughly equivalent to filling an existing 50mm cavity with good insulation.

Any new thermal elements you build will need to achieve the slightly better U-values stated in table 2 on page 16.

The possible grey area comes with if the current building isn't heated then is an existing wall a retained thermal element? Or is it a new thermal element bearing because it wasn't previously preventing heat loss.

Most architects just treat all elements as if they were new and so specify the U-values in table 2. If you run with this then you won't go wrong.

I'd like to say hope this has helped but I'm sure its just added to the confusion.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14646&Focus=248834#Comment_248834 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14646&Focus=248834#Comment_248834 Tue, 25 Oct 2016 18:58:08 +0100 neilu Tell them about your project and they will advise you on what you need to do. Obviously they will specify their own products but they do give very good advice.
I'd start with Kingspan or Celotex for rigid insulations and Knauf for mineral wool type insulations.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14646&Focus=248842#Comment_248842 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14646&Focus=248842#Comment_248842 Tue, 25 Oct 2016 20:35:34 +0100 discotroll
Just back from work and had a chance to read through all of the helpful comments.

I should have made it clear that I wasn't just looking to squeeze in under the threshold on u-values but was more genuinely confused by the array of information out there.

I agree that both kingspan and celotex sites are really good for helping get the best solution (don't mind so much them specifying their own product as it's part of the exchange, as it were).

I'll be doing the insulation/energy side of the job myself so it'll be done properly with absolutely no air gaps in the insulation materials and as close to a continuous layer between me and the outside world as possible.

right - I'm off to follow up the links supplied and do some further reading...]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14646&Focus=248843#Comment_248843 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14646&Focus=248843#Comment_248843 Tue, 25 Oct 2016 20:38:58 +0100 Nick Parsons https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14646&Focus=248844#Comment_248844 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14646&Focus=248844#Comment_248844 Tue, 25 Oct 2016 20:44:15 +0100 fostertom Posted By: neilua conversion is classed as a material change of useAng on, are we sure what's meant by 'conversion' in this case? if simply upgrade/alteration/extension it's not 'material'.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14646&Focus=248847#Comment_248847 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14646&Focus=248847#Comment_248847 Tue, 25 Oct 2016 21:09:13 +0100 discotroll https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14646&Focus=248855#Comment_248855 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14646&Focus=248855#Comment_248855 Tue, 25 Oct 2016 23:04:03 +0100 ringi (I wish I had done this!)]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14646&Focus=248858#Comment_248858 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14646&Focus=248858#Comment_248858 Wed, 26 Oct 2016 01:18:14 +0100 fostertom https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14646&Focus=248883#Comment_248883 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14646&Focus=248883#Comment_248883 Wed, 26 Oct 2016 10:58:46 +0100 discotroll
That is the way I'm planning on working - like a completely separate sealed-off inner structure where the insulation takes place and we live, with the outer original structure just supporting the roof etc and being cared for through ventilation etc between the two.

Good to know that I'm thinking along the right lines....]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14646&Focus=249076#Comment_249076 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14646&Focus=249076#Comment_249076 Sun, 30 Oct 2016 06:00:00 +0000 cjard I've probably spent fifteen thousand quid on kingspan and membranes/or on/Tescon tapes.. the icynene quote was 25k I think.. for the extra ten grand I'd have got an awful lot of my life back, probably 5 months of it.. it's hard to weigh up sometimes, because I only get 2 days a week to build, the rest is taken up with full time job so while in raw days it would have saved about 40, its one of those things where.. is it 10k for 5 months hence 25 ish grand a year, I.e. Small fry, or is it 10k for 40 days hence more like 85k a year I.e. A reasonable saving on the mortgage..

Ask my little lad, who once upon a time said "see you later, daddy going to the building site" but increasingly these days is pulling a face/crying as I leave, what he thinks the time is worth!]]>