Dan F

Passive Standard House + Integral Garage

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Hi,

 

We are now at the stage where our archtects construction drawings are being converted into timber-frame drawings and we're giving doors, windows and UFH more thought.

 

Our design has an integral garage (a detached garage wouldn't have got past planning) which means we have to work out exactly how to best treat it the garage in the contect of an airtight, highly insulated house.  In our case the garage isn't just attached, but it's integral with 2 walls being shared with house, and 60% of garage ceiling being below an upstairs room.

 

Three approaches I can think of:

- Include garage in thermal envelope:  This is the easiest from a timber-frame and insulation perspective, as the continuous layer of insulation is on all the exterior walls and a single slab foundation can be used.  The major challenges with this approach are i) ensuring thermal-bridge free garage theshold ii) finding a garage door that is insulated and air-tight.

- Exclude garage compleltly from airtighness/insulation perspective.  This involves using a seperate slab (seperated by EPC upstand) for the garage, the house->garage walls being 300mm twin-wall will full insulation (as garage is considered outside temp) and the garage roof also needing to be as insulated as possible (which hard given only 253mm deep). We could use any garage door we like, but garage would typically be close to outside temp.

- Middle of the road.  Exclude garage from thermal envelope and air-tightness layer (seperate slab also), but i) ensure external garage walls have fair amount of insulation, ii) put some thought into the threshold iii) find a fairly airtight and well insulated garage door (something like Hormann LPU67 Thermo maybe?), and iv) put UFH into the slab just in case we want to use it as anything other than a garage in the future.

 

Which approaches have others gone with?

 

 

Edited by Dan Feist

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Think I would treat the whole house as the airtight envelope, but then make sure you can divide off the garage as a separate cell, have a decent external door from the house into it, then you need not worry about the airtightness of main doors etc.

 

Heating the slab sounds nice, but unless it's a work room a bit pointless, because it will be 4" lower to meet building regs, so if ever concerted would need re-visiting then anyway

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3 minutes ago, JFDIY said:

Think I would treat the whole house as the airtight envelope, but then make sure you can divide off the garage as a separate cell, have a decent external door from the house into it, then you need not worry about the airtightness of main doors etc.

 

That makes sense yes, but because we decided to certifiy we can't have it both ways and we either need to include garage in the thermal/airtight enveolope and get a very good garage door or exclude it and use a seperate slab and full insulted internal garage walls.

 

It does make some sense, because if you don't have a really good garage door and/or garage threshold detail, then it's not really a good idea to share the garage slab with the rest of the house..

 

 

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sounds like a bad design idea to me - integral garages are on my list of in house winter cooling systems 

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37 minutes ago, tonyshouse said:

sounds like a bad design idea to me - integral garages are on my list of in house winter cooling systems 

 

I agree it's a bad idea, but sometimes planning limitations (or space) dictate things...

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1 hour ago, Dan Feist said:

 

That makes sense yes, but because we decided to certifiy ... 

 

What's the benefit of going for certification?

 

I don't believe anyone here has gone that far (I recall for us it was £2000 in specific consultant costs with no obvious benefit) and also restricted choice on MVHR / heating systems etc.

 

That said, we meet or exceed passive standards across insulation, airtightness and heating / cooling requirement so that's good enough for me.

 

Can't imagine it would increase the value of the house, perversely it would probably reduce it ...!

 

To the OT - I agree with the idea to have a decent airtight door between garage and house and then get decent Hormann insulated garage doors or equivalent.

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Ha, I knew certification isn't very popular on this forum! 🙂  We're doing it to aid in decision making and for the quality assurance, not the certificate.  It means we are sure that timber-frame and window installation detailing etc. is fully reviewed, that we're choosing the best glass specification (u/g value) and overhang sizes to best balance insulation/solar gains, and to ensure the investment in external blinds makes sense amoung other things.

 

Yes it's a couple of thousand £, but so it's the structural garantee, building control, site insurance and everything else.  And if it improves our confidence in what we're doing and potentially also our comfort living in the house for the next however many years then it's money well spent in our minds (we don't have time or knowledge to play around with PHPP ourselves).

 

Maybe I look into the Hornam spec from a u-value and airtightness standpoint, and if it's good consider including everything in thermal envelope and keeping things simple...

 

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There is a flaw in your plan.

 

While building regs don't stipulate specific ventilation requirements for a single garage (they do for a double garage) they do say you should not attempt to make a garage air tight.  But even if you tried, you will not find an air tight garage door.

 

All you can do is make ALL the walls and ceilings between the house and the garage your insulation and air tightness envelope and fit an air tight door between the house and garage.

 

And there is another problem, it has to be a fire door.  So you are looking for an air tight, insulated fire door between the house and garage.

 

I admitted defeat on that, and just fitted an internal fire door and added extra draught proofing and accept there will be some heat loss and a bit of a compromise to the air tightness.

 

You have to be realistic.  My total annual heating bill is just over £200.  Even if I could shave £50 off that by having a completely sealed air tight insulated door between the house and garage (unlikely the saving would be that much) , with such a door costing over £1000, it would have a payback time of 20 years.

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Quote

While building regs don't stipulate specific ventilation requirements for a single garage (they do for a double garage) they so say you should not attempt to make a garage air tight

 

That's a very good point, and not one I was aware of, thanks!  Will look this up to see the specifics..

 

Quote

But even if you tried, you will not find an air tight garage door.

 

That's what I heard, but I didn't know how good/bad something like the "Hormann LPU67" (which is class 3 airtightness) actually is.

 

Quote

All you can do is make ALL the walls and ceilings between the house and the garage your insulation and air tightness envelope and fit an air tight door between the house and garage

 

Yes, this is the current/default plan.  I just wanted to pick peoples brains on the alternatives....

 

Quote

And there is another problem, it has to be a fire door.  So you are looking for an air tight, insulated fire door between the house and garage.

 

Yes, was aware of this, but hadn't looked at prices yet!  This would be one reason to include garage in airtightness envelope, but as you said that not allowed due to BRegs.

 

Very useful, thanks @ProDave!

Edited by Dan Feist

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I would treat the garage as outside the heated envelope and air barrier if you must have an integral one

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Doors:

We had a quote for a PH certified airtight FD30 moralt door, about £2k from Latham's in Hamel Hampstead. Be sure to ask for unfinished ready to paint, otherwise they can be twice that price (!)

 

Otherwise we thought to put 2 doors in an "airlock" configuration, one cheapest FD30 then the cheapest passive house door we could find. The FD30 may or may not remain in the long run...... (There's minimal fire risk in our garage, it's too small for a car and we don't keep any petroleum in it)

There's also a local project I can point you at where they successfully certified by using a standard FD60 door with smoke seal and drop threshold, and glueing sheets of solid insulation panel to it and remedial work to get it airtight. This can only work if connecting to a non-inhabited room I'd imagine as it would fail the room comfort criteria.

 

Finally, cheapest option maybe no internal joining door but arrange for a pair of neighbouring external doors with a small porch/link corridor over them.

 

 

 

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On 02/01/2020 at 21:07, ProDave said:

While building regs don't stipulate specific ventilation requirements for a single garage (they do for a double garage) they do say you should not attempt to make a garage air tight.  But even if you tried, you will not find an air tight garage door.

 

@ProDave I'm pretty sure these are Scotland-only building regs.    Not saying an airtight garage with no ventilation is a good idea, just updating thread with findings.

 

Good point @joth, simplest solution to door might be just to walk outside.  Will have to look at door options and "airlock" alternative more serisouly I think..

 

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On 05/01/2020 at 09:27, joth said:

Doors:

We had a quote for a PH certified airtight FD30 moralt door, about £2k from Latham's in Hamel Hampstead. Be sure to ask for unfinished ready to paint, otherwise they can be twice that price (!)

 

@jothI just had a quote for the same door (Ferro Firesafe 826 x 2040 leaf) from a Principal Doorsets for £3500 + £500 delivery (excl VAT)!!  Also unfinished MDF.

 

What did you decide to do in the end?

 

Edited by Dan Feist

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6 hours ago, Dan Feist said:

 

@jothI just had a quote for the same door (Ferro Firesafe 826 x 2040 leaf) from a Principal Doorsets for £3500 + £500 delivery (excl VAT)!!  Also unfinished MDF.

 

What did you decide to do in the end?

 

Still planning on going with the quote we had on the Moralt, but haven't actually ordered it yet. 

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@joth, my apologies if you have answered this in another thread, but did you end up going down this route?  Did you find anything more economical?  Many thanks

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1 minute ago, tanneja said:

@joth, my apologies if you have answered this in another thread, but did you end up going down this route?  Did you find anything more economical?  Many thanks

 

We haven't ordered this yet.  But Latham's was a lot cheaper than Principal Doorsets.  Also, you don't necesarily need the PH version, the standard version is stil pretty good from u-value perspective and was £1,685 at the time (vs £2,200).

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@Dan F thank you, the standard version meaning the KlassicPlus? https://www.lathamtimber.co.uk/products/door-blanks/brands/moralt

 

Also, does it come as a full kit as one online PDF suggested (frame, seals etc) or just the blank at that price?

 

I was half considering taking a nice solid wood door then retrofitting a 5mm aerogel sheet and further thin sheet board i.e. MDF to the back to get me the insulated door, then it would be making sure the seals were up to scratch.  The passive doors seem to have a saw tooth closure with the bank of the door returning once or twice, that would be more tricky to do.

Edited by tanneja

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If those kind of prices are not just for the blank but for the frame and other bits of kit (as stated as an offered package on the german manufacturer website) that is interesting.

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19 hours ago, tanneja said:

@joth, my apologies if you have answered this in another thread, but did you end up going down this route?  Did you find anything more economical?  Many thanks

Yes we did, from Lathams.

There was a bit of a last minute flub up with it. I thought it comes in inward opening only, but when ordering our contractor saw it has outward opening too which is more convenient to use so we swapped to that (with out PH designer's blessing).  But ... this means the airtightness boundary has to pass under and through the threshold to the seal on the outside face rather than being on the inside, which our joiner was really unimpressed by and called the whole door a piece of overpriced rubbish which obviously smarts a bit after putting that much down on it. (Same feelings with the cost:quality of the petwalk door, for slightly different design shortcoming reasons).

 

So anyway if doing this again I'd keep with the inward opening door. I now really understand why passive houses prefer inward doors. It's all about the thresholds, stupid. (Well, I guess houses with airtightness boundary on the outside of the walls would prefer outward doors?)

 

18 hours ago, Dan F said:

 

68mm Ferro Firesafe EI30 (assuming you need 30min fire door).  U-value I was quoted for the whole doorset was 1.02 vs. 0.76 for the passive version.

Getting an insulated fire proof door is easy: just glue a shedload of cellotex to a cheap FD60 door and have your thermal consultant knock up an installed U-value for the result. Seen a couple houses do that. The key thing about the Moralt passive rated door is the airtightness rating. Does Ferro Firesafe have that?

But also, see my comments above..... :-/

 

2 hours ago, tanneja said:

If those kind of prices are not just for the blank but for the frame and other bits of kit (as stated as an offered package on the german manufacturer website) that is interesting.

Yeah.... it is a full doorset. It doesn't have a the eurolock cylinder nor door handle, again to my joiner's disgust, and the lock mechanism that came with it is currently removed as he was struggling to get the spring to fire reliably. I'm like sure, "add it to the snagging list".

 

Attached is the only photo I have of it.

 

 

PXL_20201016_152838960_MP.jpg

Edited by joth
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@joth i really do appreciate you sharing your experience, and am disappointed for you by the issues you have faced. Sincerely hope the house ends up as good as the progress picture implies it will be.

 

Builder is emailing Lathams tonight. Would like to retrofit strip wood to the front of it to have the porch be a strip wood facade. Hopefully all doable.

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On 19/02/2020 at 18:56, joth said:

Still planning on going with the quote we had on the Moralt, but haven't actually ordered it yet. 

Did you go with the Moralt FD30 in the end?

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10 hours ago, Adrian Walker said:

Did you go with the Moralt FD30 in the end?

Yes, see my previous response 🙂

 

On 22/10/2020 at 16:56, joth said:
On 21/10/2020 at 22:11, tanneja said:

@joth, my apologies if you have answered this in another thread, but did you end up going down this route?  Did you find anything more economical?  Many thanks

Yes we did, from Lathams

 

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