Question on What U Values = What BER Rating?

blobert

Hello,

I'm planning to build a prefabricated house.

I've been speaking to a number of prefabricated house builders in Europe who build up to German Passive standards to get a rough quote.

They have asked me "What are the expected U-values for walls, roof and windows" as they can build to various levels depending on budget.

I know as a minimum the house would need to be A3 but I'm just wondering if there are any corresponding U-values for walls, roof and windows that would equal that, and then also for A2 or A1 rated. Can't find this online but I may not be looking correctly.

The house is going to be a large bungalow with a lot of glass (most facing south but also with some facing west and a little bit north). I'm planning to have a geothermal heating system. I might not bother with solar for the moment (assuming I can still get A rated without it) and then add it later when battery storage prices reduce.

Any advice would be much appreciated!

Gumbo

Technical guidance document part L

Metric Tensor

The U-Values of the walls are only a small part of what is required to comply with the building regulations. They feed into an overall calculation with air-tightness values, heating, lighting, etc. to give an overall measure of compliance or non-compliance.

This calculation is called DEAP and it is the same calculation that is used to determine BER rating. Although you shouldn't mix up the two - you don't actually HAVE to get an A3 or A-anything else rating. You have to pass the EPC, CPC and RER tests in DEAP. (It just so happens that if you do all that you basically end up with an A3 or A2 rated house.)

So without doing the overall calculation you are shooting in the dark with regards to U-Values for fabric elements. TGD L lists some "backstop" U-values but if you blindly use those there's a fair chance you won't be able to make your DEAP calculation work and therefore not make your house compliant.

Calahonda52

German made in a German factory to Passive standard if you want it.
You would be CRAZY not to take that option.
Its not the initial extra cost you should look at, its the LCCA
https://www.wbdg.org/resources/life-cycle-cost-analysis-lcca

Who will do the slab design and install?

blobert

Calahonda52 wrote: »

German made in a German factory to Passive standard if you want it.
You would be CRAZY not to take that option.
Its not the initial extra cost you should look at, its the LCCA
https://www.wbdg.org/resources/life-cycle-cost-analysis-lcca

Who will do the slab design and install?

Thanks very much for the replies guys.

So if I can go for German Passivehaus standard you think it's worthwhile.

My understanding previously, which is probably out of date, was you could get fairly close to that standard (which would suffice from a BER point of view) but to go all out Passivehaus standard would cost a fair bit extra. If it's the case that it's only a bit extra then I'd just go with that, as you say if I wind up living there 30+ years it will probably more than even out.

Re slab design and install, some of the German companies will build here and have in house architects to advise on this. But they seem to be the pricier guys. I'm thinking it might make sense to have an Irish architect on board to liaise with their guys to make sure everything is to Irish Regs, several of the guys I've spoken to have said they can build to Irish regs. There seem to be a number of companies here that will do passive slab foundations also. So I'm guessing it would be a case of getting this work done in advance of the house arriving to sit on top of it.

At the moment I've just got a rough house design (ie by me as opposed to architect) that I'm showing to various prefabricated builders to get a rough idea of price vs a traditional build. I suspect there could be some savings in working with a Polish/Estonian/Latvian company that do this vs Germans but there is probably a bit more risk also, in that the Germans are more used to a one stop shop approach, ie they do everything for you. We'll see what the price differential is, unless there's a big saving I'll probably go with the Germans.

Calahonda52

the slab will need to be done and signed off on here to get certification on the final house
You will also need to consider other groundworks as well as good access/hardstanding for the cranes/or what ever they will use..
You will also probably need to have scaffolding lined up
IMO, the incremental cost of the PH in a factory build must be very small.
Are you going with MHVR?

blobert

Calahonda52 wrote: »

the slab will need to be done and signed off on here to get certification on the final house Ok, thanks

You will also need to consider other groundworks as well as good access/hardstanding for the cranes/or what ever they will use.. Thanks, most of the time it would be a truck with crane on, site has limited access though so may need a 2nd smaller truck/crane to take in from the street. I'll need to get the work on the geothermal done at the same time as the groundworks I'd imagine
You will also probably need to have scaffolding lined up

IMO, the incremental cost of the PH in a factory build must be very small. This is one of the things I'm interested in finding out, the saving, if any vs traditional build. In my mind there has to be a saving in somthing build in a Polish factory at local rates/materials cost and erected in 3 days here vs Irish builders working on it for months. But I could be wrong. Other main advantage is time, prefabricated house should be done completely in 3 months and less likely to overrun, this is a big advantage to me vs potentially 1 year+ for traditional build.

Are you going with MHVR? Yes, I will be. Keen to also have geothermal, both for heating in winter and to run in reverse for cooling in summer. Like I say this house will have a ton of south facing glass so I think will be prone to getting very hot in summer without this. Our current house is A3 with no MHVR, it's not even south facing and it gets unbearably hot in summer (it was 43 degrees in our bedroom when we came back from a 2 week holiday in the summer previously) so it's a big concern that the new house won't unbelievably hot in summer.

Replies in bold

MicktheMan

A properly designed ph (using phpp and local climate data) should not suffer summer overheating

sydthebeat

MicktheMan wrote: »

A properly designed ph (using phpp and local climate data) should not suffer summer overheating

I was just going to post the same.

Sounds like the OP should go down the certified passive route.

Muahahaha

Sounds like a very interesting build OP. I remember seeing that German company Hufhaus do a build on Grand Designs years back and it was impressive how fast it went up and the efficiency of the operation. Would be great if you could keep the thread updated as the build progresses as Im sure lots of posters would be interested in seeing a pre-fab build done in Ireland.

blobert

Muahahaha wrote: »

Sounds like a very interesting build OP. I remember seeing that German company Hufhaus do a build on Grand Designs years back and it was impressive how fast it went up and the efficiency of the operation. Would be great if you could keep the thread updated as the build progresses as Im sure lots of posters would be interested in seeing a pre-fab build done in Ireland.

Thanks, I got a quote from one of the higher end German manufacturers and it was absolutely crazy, including ground works etc it was about €4750 per m2 and that was not even full passive standards with less tall windows etc.

To be fair I'm planning to build pretty much the most expensive possible house according to them, a very big bungalow covered in glass windows.

I'm waiting to get rough quotes back from some Latvian/Polish prefab builders next to see how it compares. I'll also need to find an architect/engineer to wade through the various offerings to see what's what from a technical perspective and also if what they can build will be likely to conform to Irish regs, or be able to be adapted to work with them.

Will let you know if I find anything interesting!

Muahahaha

Yeah almost 5k a sqm is huge money, that would make a 200sqm house a million euro :eek:

Would imagine there are much cheaper options out there, especially with Lativan or Polish companies. I'd imagine there are companies in the UK doing it but they could be expensive too, worth looking though

One thing you might need to consider is if it is a timber frame house that the timber used is suitable for the damp and humid Irish climate.