SIP construction new build and upstairs heating

Viborbx

We would really appreciate some advice. We are getting conflicting advice from the firm that supplied the SIPs kit, our main contractor and the heating engineer. The Architect is unsure. We have had the SAP calculations done.

As a result of the SAP calculations we are required to instal an air source heat pump. It is a large two story house with a lot of East facing glazing. We have been reading the very useful information on this site and the links and it appears that the cost to run this may be high. We live in the north of Scotland.

We were initially told we would not need any heating upstairs. The main Contractor and the heating engineer wants us to put radiators in. There is underfloor heating downstairs.

Can anyone advise us as to whether or not we will need heating upstairs?

Also the Main Contractor wants us to instal a hybrid heating system. Gas boiler and air source heat pump. We feel that this is unnecessary as we were told the air source heat pump would be enough.

I hope I have given enough information and someone with experience of this can help. Thanks

ComicGeek

No, the SAP calculation won't require you to have an air source heat pump - it is just one possible solution to achieving compliance under the SAP calculation, and there will be others, ie improved insulation and air tightness, triple glazing, good levels of heating controls, roof mounted photovoltaic panels etc.

Air source heat pumps that are poorly designed and installed will cost a lot to run and will be a major problem - I certainly wouldn't specify an air source heat pump in your location.

You will certainly need heating upstairs, whoever told you that you wouldn't is an idiot.

A hybrid heating system provides tolerance if the heating calculations are incorrectly done, or if the heat pump installation is botched - it's an insurance policy for the main contractor because he knows that what has been specified has no chance of working properly.

The correct way is to specify the right heating system (which is probably a gas boiler if you have mains gas), and then see what needs to be achieved on the SAPs to make this work.

Viborbx

Thank you for replying.

We will have triple glazing and a heat recovery system.

We had wanted underfloor heating upstairs but were told we would not need it. (Nor any kind of heating!) The floor we have there will now will not support the pipes for underfloor heating.

We are so disappointed that we have been given misinformation. I will pass on what you have written to my Architect.

ComicGeek

Well, with triple glazing and MVHR you shouldn’t really have any problems getting sap compliance with air source heat pumps. Normally it’s because the sap assessor hasn’t calculated the thermal bridging part of the calc, and the overall sap result is compromised as a result. Unfortunately we have a lot of clients who use inexperienced sap assessors to give them poor advice.

Have you looked at routed chipboard systems for upstairs, that sit on top of floor joists? I find it hard to believe there can’t be any solution for ufh upstairs unless the flooring is fully finished and the ceilings below already boarded and plastered.

Is it definitely mains gas available, and not LPG? Sometimes off grid schemes are hard to comply.

Viborbx

Hi, the upstairs floor came as part of the kit. It was laid before the upstairs walls were erected on top of it.

Yes, it’s mains gas as we had a house on the site which we demolished.

We are SAP compliant but only if we put in an air source heat pump and no secondary heat source. (A gas boiler.)

I think our only option upstairs now are radiators. However, I have asked if we can get electric underfloor heating with the type of flooring laid. We are getting heating pads in the two ensuites upstairs.

System

If you've got a mhrv surely that will be controlling the temperature in the rooms upstairs?
How old is the building warrant?
tbh I don't see a problem with specifying and installing the right air source heat pump in your location, they are used all over the highlands at the moment, with a sips kit too you should be achieving a high level of air tightness so the sap should be pretty straight forward, as long as it's done right

Viborbx

It’s a new build. The kit is up and the windows are on order. The zinc roof is being installed just now.

Apparently we have to put in an air source heat pump to achieve the SAP rating. The whole front of the houses is more or less double height windows.

System

Viborbx wrote: »

It’s a new build. The kit is up and the windows are on order. The zinc roof is being installed just now.

Apparently we have to put in an air source heat pump to achieve the SAP rating. The whole front of the houses is more or less double height windows.

yeah, but how old is the warrant? there have been some slight changes in the regs over the last few years which can make the sap more or less onerous...

ComicGeek

Viborbx wrote: »

Hi, the upstairs floor came as part of the kit. It was laid before the upstairs walls were erected on top of it.

Yes, it’s mains gas as we had a house on the site which we demolished.

We are SAP compliant but only if we put in an air source heat pump and no secondary heat source. (A gas boiler.)

I think our only option upstairs now are radiators. However, I have asked if we can get electric underfloor heating with the type of flooring laid. We are getting heating pads in the two ensuites upstairs.

Electric underfloor heating is a non-starter, it will cost you a fortune to run when compared to either a gas boiler or air source heat pump. That's just making a poor design even worse. All the air source heat pump does is to artificially raise the target within the SAP, thereby making it easier to comply - it does not mean that it's a better system or more economic to run!

The SAP calculation informs the design, not dictates it. I appreciate that the building shell is virtually complete, but there is something fundamentally wrong with the SAP calculation if they can't make it work with mains gas - it would be worth getting another SAP assessor to look at it. There are varying levels of insulation in SIPS systems, but that combined with triple glazing and MVHR should be more than sufficient.

So the key questions I would ask are:

a) Have they used the correct U-values for the SIPs systems and windows?
b) Have they used the default thermal bridging values? If so, they need to complete this properly, and the SIPs provider are likely to have y-value calculations for their standard junctions.
c) Have they used a default gas boiler for the mains gas calculation that apparently fails, or an actual current boiler and cylinder?
d) Have they included the correct heating controls, ie time and temperature zone control, delayed start thermostats & weather compensators?
e) Have they set the thermal mass correctly for the building? If its SIPs then it will be a low thermal mass.
f) Is there a wood burning stove within the scheme? Has this been included as a secondary heat source?

I've done thousands and thousands of these over the last 15 years, there's something really wrong here. Mains gas would be a non-brainer for me, I wouldn't even consider air source heat pumps.

If the air source heat pumps provide at least 50.1% of the annual heat demand then you could have the gas boiler provide the remaining - this fools the calculation into setting the heat pump as the dominant heating fuel.

ComicGeek

the_r_sole wrote: »

If you've got a mhrv surely that will be controlling the temperature in the rooms upstairs?
How old is the building warrant?
tbh I don't see a problem with specifying and installing the right air source heat pump in your location, they are used all over the highlands at the moment, with a sips kit too you should be achieving a high level of air tightness so the sap should be pretty straight forward, as long as it's done right

The MVHR won't have a heating coil for a standard system - it's only Passivhaus type systems that would use the supply air for heating, and they would pass Bldg Regs by a mile without all the issues noted by the OP.

If the OP was looking at air source instead of oil/LPG I would agree with you - but mains gas is still cheaper to install and run than air source. The problem is that the SAP hasn't been done correctly, and this has led to a bad decision - it needs to be unpicked and reviewed again.

Viborbx

Sorry, I misunderstood. The Building Warrant was issued in 2016.