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Architects help! U values (exciting)

(12 Posts)
betterwhenthesunshines Mon 15-Oct-12 17:55:01

We had an architect work on our renovation project (it took a looong time due totheir other work commitments). Then they pulled out after tenders were submitted so we have progressed with a surveyor doing the contract admin.

The contract is for Minor Works with Contractor Design and the main contractor is using a sub contractor for mechanicals.

We plan to have a new woodburner (specified) which should be linked with solar thermal tubes (existing) to an accumulater heat bank (specified as Excel or similar) and a new oil fired boiler which will kick in if the woodburner is not active. Work has started but we had a meeting to discuss radiator sizes etc and it bacame apparent the subcontractor had not even understood a thermal store was required. Now the contractor is saying it is down to the architect to supply Uvalues and until this is done he can't work out heat loss and design the system specification. He mentioned a 300L store, my research has advised a 750L store so there is a huge discrepancy.

Whose responsibility is this? We have paid a lot of fees for preofessional services and a reputable builder and now I'm feeling slowly throttled....

tricot39 Mon 15-Oct-12 20:48:20

The heating engineer needs to know about the u values in order to design the system as it affects the expected heat loss. In other words the higher the u values, the higher the heat loss, the bigger/more powerful your system would have to be.

A quick call to the architect should establish whether he used part l of the building regs as a minimum or whether he upgraded to put in extra over. Either way you will get the info to pass on to the builder. If you don't want to call him you would need to get the wall/floor/roof construction details and insulation spec/thicknesses and send them to the insulation manufacturer in order for them to advise.

discrete Mon 15-Oct-12 20:56:44

The thermal store will mostly affect how much heat can be stored, and that will (usually) be linked to the area of solar panels rather than the u values, afaik.

There is no point in having a 750l store if your panels can never heat it up, and it would be incredibly wasteful of your solar panels (and money!) to have a 300l store if they can easily heat much more....

You do need the u values to decide how many radiators etc. you need, granted although you could do it like I do and just wing it but the store is a separate issue.

betterwhenthesunshines Mon 15-Oct-12 21:11:02

Thanks tricot - apparently the architect did mumble something to the contractor this afternoon about having done them, but not sure if he could find them hmm. Will give him a day to go rummaging through his files and then chase on Wednesday I think.

And the thermal store - the main input will be a woodburner that sends 14kW to heating system ( plus 5kW to room) at full whack. The solar thermal is more low level back up, although in the summer it used to heat the old HWC up to 65 degrees. So it needs to be big enough to store this for a round of central heating and showers the next morning. The advice from the woodburner heating engineer was for 750l based on information I gave him about room sizes, ceiling heights etc. discrete do you have a thermal store?

It's quite hard finding any sort of definative answers !

betterwhenthesunshines Tue 16-Oct-12 16:44:09

please help! <desperate>

The architect says the spec requires the contractor to supply U values. The contractor says its not his responsibility - it should be part of the building design process to ensure it passes Building Regs. ( He says he didnt raise this earlier as U values are mot mormally submitted with the tender documents but are supplied to the contractor on request in the early build stages.)

We have Building Regs Approval with a condition of supplying a SAP report. I thought a SAP report was a calculation to show the windows are compliant. Does this mean we have ordered windows that won't pass approval? Is this why the architect pulled out?

Does anyone know anything about this? Who does U value calculations?

Pendeen Tue 16-Oct-12 17:03:45

SAP calculations are usually best done by a specialist. They cover all the energy and insulation aspects of a project - not just windows.

Goolge will give you a list.

As an aside, if I had designed your renovation project I would have pulled in a building services engineer for advice at some stage as much of the Building Regs 'Part L' requirements are becoming too specialised for us simple architects especially if you as client want a very energy-efficient property.

tricot39 Tue 16-Oct-12 18:08:01

Aside from building services advice which is sensible with complex systems, whoever specified the windows and insulation elsewhere has fixed the u values. They should be responsible for stating what they worked to. Unless you have a complex form of contract not normally found on domestic projecs this responsibility will lie with the architect. However if he confirms that he has specified building regs minimums then you can pick this off tables, or ask insulation manufacturers as i previously mentioned. The main thing is tho that if the architect said in his spec/drawings what thickness of insulation was to be used or they type of glazing he should be providing the u values. It is not for the contractor to specify.

discrete Tue 16-Oct-12 18:22:07

yes, I do have a thermal store. A 500l one.

WithManyTots Tue 16-Oct-12 19:47:26

In our case the architect calculated all the U values and this was part of the information submitted before the build for planning and building control. It is a relatively simple calculation once you have all the detailed information, sizes, materials etc.
Did your architect go this far for you, in which case he should be able to do it, or was some left for the contractor to decide, in which case he should be able to do it?

betterwhenthesunshines Tue 16-Oct-12 21:09:29

Thanks all - it sounds as though the architect has been somewhat amiss, even if only to recommend that this should have been looked at by services engineer as you say Pandeen. I was asking about all this stuff in Fenruary and he said "no, we just set specification guidelines" It also sounds as though he MUST have done some sort of Uvalue calculations for building regs - will chase that up tomorrow.

If not, how have we got an OK on building regs? (SAP calculations excepted - not sure when this should have been done - surely the architect should have taken control of commissioning this if it was required?) The architect says the extension part of the renovation is "in excess" of building regs. So if he has this information , why is he not providing the calculations???

Very frustrating - Pandeen, can you come and work for me? ;-)

Pendeen Wed 17-Oct-12 12:52:15


Thanks for the invite smile

Although manufacturers of building products may quote 'U' values this is only the start of the process because the overall 'U' value of the building element (e.g. a wall) includes such factors as surface resistances, cavities, cold bridges, insulation and a host of other complications. Suppliers tend to be happier quoting 'K' values instead because these do not depend upon thickness and the other factors.

From there, the architect (or whoever) has then to calculate the total 'U' value for the project - and for an extension then look at the effect on the whole house. For a renovation project the Building Regs include work to existing 'thermal elements'.

Then there are the questions of air leakage, boiler efficiencies, etc.

Going beyond 'U' values and on to calculating a SAP rating is - as I mentioned above - a nightmare and best left to specialists.

Oh and BTW - the approval you have is 'conditinal' so it's perfectly valid but they will not give you a Completion Certificate without the conditions being discharged.

Your architect has been a little naughty I feel, but that's only my opinion. We really should have to continually assess our limits as regards overall and specific competency and I for one know that delving too far into Part 'L' is a sure recipe for headaches and frustration!

Hope all this helps and, best of luck...

betterwhenthesunshines Wed 17-Oct-12 15:05:11

Thank you - our surveyor/ CA is currently looking into getting SAP calculations done by a specialist. But yes, it had better work out OK or the architect will have designed an extension that isn't compliant which would be a fairly useless piece of design.... it was naughty of architects to simply hand over when they pulled out without highlighting all this I think.

I am hoping that the upside of discovering all rotten floor joists and therefore highly expensive replacement with insulated solid floor construction may now turn out to be a benefit <trying to look for silver linings>

Now onto the issue of what has been 'specified' regarding the heating system.....

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