Thermal Calcs - SAP 2009

[MdB]

I'm in the process of working out some drawings for an extension and as we want a lot of glass, the thermal calcs are rather important. I spent a while looking for software which will do the calcs for me whilst I'm exploring options (rather than pay somebody to do it properly) and came across this: http://www.rusfa.com/downloads.htm

sap916.zip isn't the finest piece of software ever but it appears to do the job and the demo version seems to have a bug which allows you to save your work using save as which is shouldn't do.

If I've put all the info in correctly, my house has gone from a SAP rating of 6/100 when we bought it to a SAP rating of 62/100 now. With the extension and other improvements, this should go up higher - even with all the glass though I have yet to work out all the details.

Might be useful for one or two of you out there anyway.

 

[Penners]

the demo version seems to have a bug which allows you to save your work using 'save as' which it shouldn't do.

Although, now that IT sleuth MdB has publicised this slip-up, we'd best download the demo as quickly as possible, before the bug is fixed! :wink:

 

[Zebra]

Why only yesterday I was considering getting such a piece of software, to save me having to make a nuisance of myself with asking various suppliers to do U-value calcs for me every time I change my mind about what to use! Does the one you got do dewpoint calculations for various build-ups? Does it have "eco" products like wood fibre in its database?

I was looking at getting this: http://www.builddesk.co.uk/our+software but may have to wait until I get my poor creaking laptop rebuilt cos I don't think it will cope!

 

[MdB]

It doesn't appear to do dew point calcs. I'll have a look later for materials in its database though it does appear to have quite a lot. If types are missing then you can always add your own.

I might have a play with the builddesk software later - it does appear to be more modern though it is 2005 rather than 2009 regs. It will be interesting to see if there is a big difference in the results.

 

[AMc]

MdB - I assume you know about using "whole house" calculations instead of elemental ones to show compliance for a big glass room (IIRC you have a "green" heat source)?

I have a professional SAP to 2006 for my house with the proposed (now completed) work done inc. our big glass room. The calculated heat requirements were completely out of whack with the actual performance despite me exceeding the specifications for insulation everywhere there was scope.
As all my heat is electric I now have over a complete year of running costs. My Good Energy electricity bill shows my total electrical power consumption is about the same as the estimated space heat load. Obviously there is normal domestic consumption to exclude but either my Air Source Heat Pump is running at a coefficient of about 1.2 or my heat load is substantially higher than models suggest.

If I were you I'd use the tool as a guide to get the building control approval then assume it's an under estimate on a period house.

 

[MdB]

MdB - I assume you know about using "whole house" calculations instead of elemental ones to show compliance for a big glass room (IIRC you have a "green" heat source)?

Yes. That was what started it all as I knew that the glass wall by itself won't pass.

If I were you I'd use the tool as a guide to get the building control approval then assume it's an under estimate on a period house.

Wise words. The big question in our calcs is the U value of the old stone wall (about 25% of the total wall area). The software offered a value of 2.2 which I used but I doubt it is correct. Fortunately, one of the walls will become an internal wall after the modifications so will be less of a heat loss.

 

[Zebra]

Dammit! The software doesn't have any of the materials I want to use! No wood wool, wood fibre, triso super 10... You can add your own but you'd have to know the insulating values (Lambda values?) and not being very up on this I'm not sure I'd get it right. Hmmmmmmmmmm........

 

[biffvernon]

Dammit! The software doesn't have any of the materials I want to use! No ... triso super 10...

You really don't want to use that.

 

[AMc]

Dammit! The software doesn't have any of the materials I want to use! No wood wool, wood fibre, triso super 10... You can add your own but you'd have to know the insulating values (Lambda values?) and not being very up on this I'm not sure I'd get it right. Hmmmmmmmmmm........

You should be able to obtain U or R values from the manufacturer and (unless I'm mistaken which is always a possibility) if they aren't BRE accredited you're going to have a tough time getting building control to accept them as contributing to compliance with Part L1B.

I'm with Biff about triso super 10 BTW - I've seen a lot of dispute about its use and very little real indication it works as suggested YMMV

 

[Penners]

I'm with Biff about triso super 10 BTW

Ditto.

 

[Flyfisher]

I'm with Biff about triso super 10 BTW - I've seen a lot of dispute about its use and very little real indication it works as suggested YMMV

It has its uses. I used it to create a 'warm roof' on the C16 part of our GII* house. We have three attic rooms up there but could see daylight between the pantiles - and not just in the areas where the tiles had slipped!

The problem was to properly weatherproof and insulate the roof while minimising the 'lift' to the tiles, which would have disrupted the eaves and gable detailing.

The eventual solution was to strip the roof, cover with 12mm WBP plywood, cover with triso super 10, counter-batten, breatheable membrane, tile-battens, re-tile. This limited the lift to less than two inches and is effectively invisible.

I've no idea of the actual thermal performance of the roof, except that it's very much warmer (and drier!) in the attic rooms than before - and probably in the entire history of the house. Fortunately, there was no BC involvement so no thermal calcs to be signed off, though it was, of course, all done with the appropriate LBC.

 

[oxalto]

I'm with Biff about triso super 10 BTW - I've seen a lot of dispute about its use and very little real indication it works as suggested YMMV

It has its uses. I used it to create a 'warm roof' on the C16 part of our GII* house. We have three attic rooms up there but could see daylight between the pantiles - and not just in the areas where the tiles had slipped!

The problem was to properly weatherproof and insulate the roof while minimising the 'lift' to the tiles, which would have disrupted the eaves and gable detailing.

The eventual solution was to strip the roof, cover with 12mm WBP plywood, cover with triso super 10, counter-batten, breatheable membrane, tile-battens, re-tile. This limited the lift to less than two inches and is effectively invisible.

I've no idea of the actual thermal performance of the roof, except that it's very much warmer (and drier!) in the attic rooms than before - and probably in the entire history of the house. Fortunately, there was no BC involvement so no thermal calcs to be signed off, though it was, of course, all done with the appropriate LBC.

Wonderful to hear this as I have to do exactly the same thing as you FF, and I'm hoping that it will improve matters as it did for you, even if it doesn't quite do as much as it claims to do. I guess the problem is that there is always going to be a limit to what can be achieved with 30mm of insulation, as well as rival companies who don't like to hear that their products are less good! Any insulation will be better than none for me!

 

[Keithj]

When we replaced the concrete tiles on our house with pantiles, we ran into the Building Control folks and their rulebook. We were told we had to fit Celotex between the rafters, and Triso Super 10 on top (under the tiles).

There were no gaps between the rafters to accommodate the Celotex (the ceilings rather got in the way) so we were delighted to be told that the Celotex could be omitted. The Triso was mandatory (or so 'twas said). Apart from making the roof a few mm higher (so the gutters had to be raised to catch the rain) it seems to have done a job. We no longer get cold draughts through the roof (although it is "summer" right now).

It struck me as a bit silly to put all that insulation into the roof, when the walls have gaps through which daylight can be seen, and the windows are "not allowed" to be double glazed*.

But rules is rules...

Keith
_____________________
* Happily, most of the existing windows, which are deemed to have been there when the property was listed, were already double glazed.

 

[Penners]

It struck me as a bit silly to put all that insulation into the roof, when the walls have gaps through which daylight can be seen, and the windows are "not allowed" to be double glazed*.

But rules is rules...

Alternatively you could argue that the heat leakage through the walls and windows makes it even more sensible to put in as much insulation as possible in other areas.

 

[AMc]

I'm glad that it works for some people, but my reading is this has solved ventilation losses in draughty roofs/rooves?
That's not to suggest any insulation and draught proofing are to be sniffed at, every little helps.

 

[Flyfisher]

I'm under no illusion that simply draughtproofing our roof made a large, perhaps the largest, contribution to its thermal performance. I would also guess that 12mm of ply has had quite an effect. But, given the space constraint, I'm not aware of anything better than triso super 10 in this application - even if it doesn't quite meet the stated performance - so, given that it adds relatively little time and cost when stripping and rebuilding a roof, it seemed a reasonable thing to use.

 

[oxalto]

I'll let you all know what I think of Tri Iso in the winter. I'm with FF though - what else are we to use when we've only a thin space available? I'll also tell you what I think of the hemcrete panels that I shall be installing once our timber frame repairs are complete.

 

[Zebra]

The reason in my case that I'm considering Triso Super 10, is that

1. The Thermafleece technical support guy recommended it
2. I want to expose the ring beam at eaves level. So I don't want to bring the ceiling on the pitched section down below the rafters too much, or the beam will be lost, or reduced to a mere sliver of exposed wood.
3. With the minimal rafter depth that I have on my sloping roof section, the Triso Super 10 (apparently!) in conjunction with 50mm Thermafleece Ecoroll gets me to a U-value of 0.15, although I've been unable to verify this independently (thus the foray into finding software to do the calculations myself!)
4. Building Control are not involved, and as far as I'm aware they don't have to be for this, although I've asked them for verification...

I hear what you're saying, Biffvernon, AMC et al, that it might not be all it's cracked up to be. Any other suggestions? My rafters are 75mm deep. I understand that 50mm celotex or similar between the rafters and 25mm under, taped at joins, then plasterboard and skim gets me to a U-value or 0.29, which is not too bad.

 

[AMc]

I would only use thermafleece if I were rich and breathability was a concern - in my place it isn't thanks to the materials used elsewhere.

Where space is completely constrained I would use multifoil as a supplementary product. It was very heavily hyped and one builder recommended it to me as the "only solution I'd need". Then (working from memory) BRE or Building Control withdrew support for it as a solo solution following some very heated (cough) debate about the testing mechanisms used to "prove" it worked. All this took place before I worked up detailed plans and got my SAP calcs for my permission.

In the end we took the decision to raise the roof with 50mm of Ecotherm between and 90mm above the rafters. It wouldn't suit everyone but our roof had been messed about a lot and headroom underneath was limited already. We also didn't need to expose rafters as the original lath and plaster (long gone) ceiling was underneath the structure to begin with.

I stuggle with idea that 50mm of wool and tri iso is going to outperform 25+50mm of kingspan/celotex/ecotherm but I could be wrong.

I would go with kingspan/celotex/ecotherm between the rafters and foamed into place then board at right angles with insulation backed plasterboard to minimise potential gaps (assuming your rafters are set at spacings that make that practical).

I would recommend you pop over to the Green Building Forum and take a look at the discussion on insulation you should find some people exploring your options
You might be interested in this massive thread on multifoil from a friend of this forum .
http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&page=1#Item_0

What U value are you quoted for the multifoil and has it been verified by BRE?

 

[Penners]

Where space is completely constrained I would use multifoil as a supplementary product.

That exactly sums up my views. Of course it's better than nothing, where you have precious little space for anything else. But I would only use it as a last insulation resort.