Green Building Forum - SAP calculations and the effect of rising heat Tue, 19 Dec 2023 05:32:59 +0000 http://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 SAP calculations and the effect of rising heat http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234138#Comment_234138 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234138#Comment_234138 Mon, 28 Dec 2015 17:53:02 +0000 vord
For a completely uninsulated old solid brick house with 100mm insulation between rafters in the loft it comes up with:
Walls: 30%, roof: 12%, windows: 34%, floor: 23%

I have upgraded most of the loft to 300mm insulation. The heating upstairs (zoned and reasonably well controlled) no longer comes on at all. Heating bills appear to be less than half what they were immediately before I insulated (though it is very warm this winter). I am convinced the insulation has reduced heating by more than 8% - with that tiny reduction the heating upstairs would still be on but it isn't.

I think the issue is that heat rises. The SAP calculations (and my own) don't appear to take any account of this. How would you go about plugging the effect into your own calculation?

Or does anyone have anecdotal evidence that could prove my calcs that suggest insulating the ground floor but leaving the roof poorly insulated would have a far greater effect than insulating the roof and leaving the ground floor un-insulated?]]> SAP calculations and the effect of rising heat http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234139#Comment_234139 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234139#Comment_234139 Mon, 28 Dec 2015 17:56:41 +0000 tony
Hor air rises, hear moves by conduction and radiation too.]]> SAP calculations and the effect of rising heat http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234140#Comment_234140 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234140#Comment_234140 Mon, 28 Dec 2015 18:26:32 +0000 Gotanewlife Posted By: vordWalls: 30%, roof: 12%, windows: 34%, floor: 23%
What sort of windows/glass do these figures use Vord? You've pretty much described my house there :cry:
However my roof is actually ERI (ie not EWI!) of 100mm EPS and I have replaced almost all the glass in the top floor for Ug 1.1 DG (from 1 x 3mm pane) and right now we are getting so much solar gain that with the heating on downstairs (needed) but off via TRVs upstairs (pretty much off anyway) it is too hot in the bedrooms - so must be rising heat (ie via hot air, conduction (I have heavy solid ceilings/floors) and radiation).]]> SAP calculations and the effect of rising heat http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234141#Comment_234141 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234141#Comment_234141 Mon, 28 Dec 2015 19:07:35 +0000 DarylP Also, ground floor U-values are calc'ed in a different way from other thermal elements, the P/A ratio?
SAP does not allow for heat/energy/warm air migrating from the downstairs to the upper storeys, it assumes the whole dwelling heated consistently.

What are you trying to achieve with your calcs?]]> SAP calculations and the effect of rising heat http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234145#Comment_234145 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234145#Comment_234145 Mon, 28 Dec 2015 19:22:58 +0000 Ed Davies
Still, looking at http://www.degreedays.net/ might help. For the weeks from the beginning of September to the end of the year for RAF Benson in Oxfordshire heating to 15.5 °C required 733 degree days last year and 515 this year. Add a bit more solar gain this year, perhaps, and it could go most of the way to accounting for your heating difference even if you hadn't insulated the loft.

What airtightness did you assume for the house? Have you done anything (other than adding the loft insulation) to improve airtightness over the year?]]> SAP calculations and the effect of rising heat http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234146#Comment_234146 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234146#Comment_234146 Mon, 28 Dec 2015 19:44:27 +0000 vord
I still don't believe the SAP calculation (never mind my own which is intended to improve my understanding and decision making). If I were living in an upstairs flat my gut feeing is I would insulate the loft to death and let the downstairs flat pay for my heating. SAP says that wouldn't work.]]> SAP calculations and the effect of rising heat http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234149#Comment_234149 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234149#Comment_234149 Mon, 28 Dec 2015 20:47:26 +0000 tony

You think SAP is bad try using EPC software... Worse]]> SAP calculations and the effect of rising heat http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234150#Comment_234150 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234150#Comment_234150 Mon, 28 Dec 2015 20:55:18 +0000 SteamyTea
I would think that my windows dominate heat losses. Not that they are particularly bad, just that I have a lot of them exposed to the outside world.]]> SAP calculations and the effect of rising heat http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234152#Comment_234152 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234152#Comment_234152 Mon, 28 Dec 2015 23:38:07 +0000 gravelld SAP calculations and the effect of rising heat http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234161#Comment_234161 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234161#Comment_234161 Tue, 29 Dec 2015 17:20:06 +0000 vord
I will need to think about the ground floor concrete covering. I copied a u value from the SAP calculation but would be better to treat it as a big middle bit which doesn't matter much and a boundary that does matter. I'm not planning to insulate the floor as I don't have much in the way of foundations and would need to underpin if I dig down enough to meet regs. Walls and windows will be insulated in the coming year and it does sound like that will help. Popped down to look at some secondary glazing this morning which should do the job.

Completely off-topic, but are there any practical issues in having an E coating on the secondary glazing? How resilient would the e-coating be to a wipe with some window cleaning stuff once a year?]]> SAP calculations and the effect of rising heat http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234162#Comment_234162 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234162#Comment_234162 Tue, 29 Dec 2015 17:30:00 +0000 Nick Parsons SAP calculations and the effect of rising heat http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234164#Comment_234164 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234164#Comment_234164 Tue, 29 Dec 2015 17:49:05 +0000 vord
I have been agonising over secondary glazing. I have a couple of beautiful arts and crafts leaded windows on the ground floor over 100 years old. The windows are fixed but I feel some sort of lift out secondary glazing would be useful for maintenance and for clearing condensation or replacing bags of silica.

I had thought about a custom frame with fixed glass. My current compromise thinking is to fit aluminium lift out and sliding secondary glazing with bits of custom frame and try to hide it all with a timber moulding nailed to the front.]]> SAP calculations and the effect of rising heat http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234166#Comment_234166 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234166#Comment_234166 Tue, 29 Dec 2015 19:08:56 +0000 djh Posted By: vordCompletely off-topic, but are there any practical issues in having an E coating on the secondary glazing? How resilient would the e-coating be to a wipe with some window cleaning stuff once a year?
There are two types of low-E coating: hard and soft. As far as I understand it, soft coat is more efficient and is what is used in modern double and triple glazing but it does need to be protected. Hard coat (e.g. Pilkington K glass) is a bit more durable I think and may cope as the inside face of secondary glazing as long as you take care of it if you remove and store it in the summer. Check with the manufacturers, I'm sure there's more than one.

I have been agonising over secondary glazing. I have a couple of beautiful arts and crafts leaded windows on the ground floor over 100 years old. The windows are fixed but I feel some sort of lift out secondary glazing would be useful for maintenance and for clearing condensation or replacing bags of silica.

My father fitted secondary glazing in our house when I was a kid. It used a plastic channel around the glass and clips screwed to the frame that held it in place. It worked very well. In particular, if fitted on a dry day in late autumn there was no condensation until it was removed in spring.

I had thought about a custom frame with fixed glass. My current compromise thinking is to fit aluminium lift out and sliding secondary glazing with bits of custom frame and try to hide it all with a timber moulding nailed to the front.

I'd expect that you need to open those and wipe them every day to remove condensation. At least that's what we had to do in our rental place.

I'd look for some solution that used timber and/or some plastic to frame the secondary glass. Try to get a reasonably airtight seal to the original frame if you want to avoid condensation. Magnetic seals can work quite well - either the long magnetic strips sold for the purpose or the small button 'super' magnets. It depends what you can accept in the way of alterations to the existing window.

Nick's suggestion sounds sensible.]]> SAP calculations and the effect of rising heat http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234170#Comment_234170 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234170#Comment_234170 Tue, 29 Dec 2015 19:41:50 +0000 Nick Parsons
I'll have to ask my cabinet-maker colleague who made the last units. He may have some pics. I am rubbish at taking pics!

''Nick's suggestion sounds sensible.''

Always a first time!:bigsmile:]]> SAP calculations and the effect of rising heat http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234190#Comment_234190 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234190#Comment_234190 Wed, 30 Dec 2015 14:34:02 +0000 gravelld SAP calculations and the effect of rising heat http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234193#Comment_234193 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234193#Comment_234193 Wed, 30 Dec 2015 18:09:14 +0000 vord SAP calculations and the effect of rising heat http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234198#Comment_234198 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234198#Comment_234198 Wed, 30 Dec 2015 22:28:39 +0000 tony SAP calculations and the effect of rising heat http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234200#Comment_234200 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234200#Comment_234200 Wed, 30 Dec 2015 23:07:58 +0000 mike7 Posted By: gravelldI stick p strip draught excluder between the plastic secondary frame and the timber windows. The screws then provide a compression seal. Works well, but remember there's also moisture ingress from outside you have to consider.


I also use p strip draught excluder, but with no secondary frame at all. The p strip is stuck to the original window frame (so you don't see the sticky stuff turn yellow) and the glass edges are stoned off and secured with modified T&E cable clips. Low cost, low labour and very unobtrusive. An 8mm hole drilled from the airgap downward to outside seems to be all that's needed to prevent condensation if the seal is good.]]> SAP calculations and the effect of rising heat http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234204#Comment_234204 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234204#Comment_234204 Thu, 31 Dec 2015 09:24:30 +0000 gravelld SAP calculations and the effect of rising heat http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234205#Comment_234205 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234205#Comment_234205 Thu, 31 Dec 2015 09:27:07 +0000 gravelld Posted By: mike7
I also use p strip draught excluder, but with no secondary frame at all. The p strip is stuck to the original window frame (so you don't see the sticky stuff turn yellow) and the glass edges are stoned off and secured with modified T&E cable clips. Low cost, low labour and very unobtrusive. An 8mm hole drilled from the airgap downward to outside seems to be all that's needed to prevent condensation if the seal is good.sounds good but not sure if I could bring myself to introduce that bypass even if it is the sensible thing to do!

I remove the secondary frames outside of the heating season so don't want to stick on the timber frames.]]> SAP calculations and the effect of rising heat http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234224#Comment_234224 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234224#Comment_234224 Thu, 31 Dec 2015 17:19:53 +0000 Gotanewlife Posted By: gravelldClean up and seal with glazing silicone?Yes and no. My panes were just slid into slots in my frames from above - free to rattle around in any wind!!! (as was the way 40 years ago here in Italy). I cleaned up and sealed with silicone - quickly got the knack and did an excellent job BUT such work is strictly temporary. The silicone gets dirty, peels back, goes milky: it is simply inevitable when silicone is used in this fashion. There some newer crystal rather than transparent/clear 'silicones' and these cost more and last commensurately longer. BUT still temporary and how long is the piece of string, depends on the location, cleaning regime, skill of putting it on, prep, and of course your tolerance for deteriorating silicone around windows. I am not saying don't do it - esp as the only better alternative is to refit all the glass, just be aware.]]> SAP calculations and the effect of rising heat http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234235#Comment_234235 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234235#Comment_234235 Thu, 31 Dec 2015 23:43:18 +0000 gravelld
What do you mean by crystal? Polymer?]]> SAP calculations and the effect of rising heat http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234242#Comment_234242 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234242#Comment_234242 Fri, 01 Jan 2016 11:34:30 +0000 vord
Assuming constant temperature inside it looks like I would have reduced the heating bills by 38% by roof insulation. (In real life it will be less due to closed doors and heating zoning and the fact I've not quite finished an awkward crawl space, but I'm more motivated to do it now).

It's useful to have a spreadsheet to fiddle around - it won't be a perfect model but should help indicate where I can grab a bit more improvement for little effort.]]> SAP calculations and the effect of rising heat http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234259#Comment_234259 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234259#Comment_234259 Fri, 01 Jan 2016 19:20:02 +0000 gravelld SAP calculations and the effect of rising heat http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234269#Comment_234269 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234269#Comment_234269 Sat, 02 Jan 2016 02:35:34 +0000 Gotanewlife Posted By: gravelldWhat do you mean by crystal?Crystal is the colour. ie normally they say transparent or clear but crystal is even more transparent and IME stays that way longer but let's not hijack the thread.]]> SAP calculations and the effect of rising heat http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234271#Comment_234271 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234271#Comment_234271 Sat, 02 Jan 2016 08:47:03 +0000 vord
Posted By: gravelldI still don't understand why the rooms upstairs don't need heating! Are the attic roofs that you've insulated sloping so there's little wall space? Are there not many windows?


I've got a zoned heating system with upstairs temperature set slightly lower than downstairs. Previously the heat loss through fabric was 57% first floor and the rest ground floor. After fixing the loft and before doing anything about windows and walls it should now be only 29% first floor (my calcs rather than anything fancy). I think the heat going in downstairs is now enough to heat upstairs, but it doesn't get too hot up there.

The house does have an unusual layout which will increase heat loss to upstairs - there is a false ceiling under a void which used to be a double height ceiling so downstairs will heat the internal walls upstairs as well as the floors.]]> SAP calculations and the effect of rising heat http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234278#Comment_234278 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13916&Focus=234278#Comment_234278 Sat, 02 Jan 2016 11:47:35 +0000 gravelld