Roof ventilation

[Gilesda]

Hi all.
Does anybody know of an easy way to cross ventilate an attached flat garage roof.
I want to insulate & plasterboard part of the roof but ventilating the voids formed after I fix the boards is a problem.
The roof joists run across the garage from an outside wall to the house itself. Fixing vents to the garage outside wall is fairly easy, but at the house abutment it's a different story.
Obviously the vents (25mm continuous) will have to be in the roof deck & close to the house wall.
Any help much appreciated.

 

[oddballodd]

Had to do this for my garage conversion, look here:

http://www.ubbink.co.uk/roof_vent/slope/abutment.htm

a few manufacturers do them

 

[Gilesda]

Thanks oddball, but my roof is flat & that type of vent is for a mono pitched, roof abutment.

 

[^woody^]

If you fill the roof void entirely with insulation, you will form sort of warm deck/compound roof, and this will not require ventilating as it will not get any condensation forming within it.

 

[oddballodd]

I tried that in my designs and the BC office told me no as it requires insultation above the plyboard to be a warm deck... that means refelting the entire flat roof....

I am sure that Ubbink do a flat roof one as that is where my installer got his from. Might be worth a call to them. I think that Timloc do one too.

Alternatives are mushroom vents, but they are a little uggly

 

[oddballodd]

Found it:

http://www.ubbink.co.uk/roof_vent/flat/felt.htm

Click on the 'Fascia Vent' tab. Its code is FRVA

 

[^woody^]

I tried that in my designs and the BC office told me no as it requires insultation above the plyboard to be a warm deck... that means refelting the entire flat roof....

The BCO was wrong.

The idea is to prevent condensation and associated rot. If no condensation can form then it's an acceptable method. Yes, it will not be a warm deck in the traditional sense, but its not far off

When doing conversions - eg garage to habitable rooms, this is what you do, and you dont have to touch the roof covering

 

[Gilesda]

I'd seen the mushroom type vents but I woulld need one for each void formed by plasterboarding the roof. I also thought a row of those would look pretty ugly.
The ubbink ventilator in your link looks like my only option. I've found similar by other companies, but they all seem to fix the same way.
You have to cut a slot in the roof decking close to the wall & fit a wooden upstand in front of the slot as pictured in the links below.

http://www.cavitytrays.co.uk/pdf/ventilation/ravfl_rev.pdf

http://www.ventspecialists.co.uk/R___B_Catalogue.pdf

The ubbink info is on page 34 in the above link.

The way my joists are fixed to the house means I can't cut a slot in the deck within about 50mm of the house wall. The garage roof joists are fixed to a lenght of 5x2 which runs the full lenght of the garage wall.
Looks like easy fit isn't an option & I've got a fair bit of work to do.

One other thing if I did use the mushroom type vents would the round hole be classed as a "continuous gap?

Woody. Would that insulation have to be spray foam to make sure every gap is filled? I notice they use that idea in Canada, I've seen it in a programme called "holmes on homes" on tv

 

[Deluks]

Woody. Would that insulation have to be spray foam to make sure every gap is filled? I notice they use that idea in Canada, I've seen it in a programme called "holmes on homes" on tv

On this site people usually compare spray foam to such evils as Hitler, Stalin and James Blunt, but they are usually referring to pitched roofs with slate or tile covering.

If vapour barrier was used tight up against the plywood, sprayed, then another vapour barrier put under the foam, I don't see as it would be a problem. But considering the potential price of having it done (god knows how much, but probably high) it would be cheaper and easier to order some celotex/kingspan from your local builders merchant and fit them in yourself.

 

[Gilesda]

it would be cheaper and easier to order some celotex/kingspan from your local builders merchant and fit them in yourself.

So can the voids between the beams be fully filled with celotex or Kingspan & not bother with ventilation?
Every website I've looked at said the voids should be cross ventilated above the insulation, below the roof deck.
Apart from what Woody said about packing the insulation in I've never came across that opinion on any site.

 

[^woody^]

If you are building new, then you either form a warm or cold deck roof and ventilate or not as the case may be. And this is what the websites will tell you.

If doing refurb, or alteration then its a compromise. And the solution comes from experience and not web sites

As I said, you only ventilate to prevent condensation build up. If you prevent the possibility of condensation in the first place, then you remove the need to ventilate.

You may not be able to fill voids properly with a solid insulation board. If you can get it tight under the deck, and up against the joists then thats fine.

If not, then Rockwool or fibreglass quilt will have to be used. But, a quilt on its own may not be enough insulation as the depth of the roof is not deep enough to allow it to be fitted in sufficient depth to meet current regs. So, you may have to combine the two, so that a quilt is used to fill the voids, and then a solid board is used to get the insulation values.

In any case, the idea is to remove any voids, and get the insualtion up against the deck to prevent any cold surfaces

 

[Gilesda]

Thanks for that info woody.
It will be difficult to pack it all with solid boards because although the joists are 5"x2" I have to fix battens to take out the 3" fall in the roof, in order to get a level ceiling. So the voids will be 5" at one end & 8" the other end. A mix of solid insulation & fibre should get around that problem though.

You mentioned regulations & that's something else I'm trying to find out about.

My garage is accessed from the kitchen & the back of the garage has been converted into a utility room, this room then leads out into the back garden.
It was converted by the previous owner at least 20 years ago but he put in no insulation & just painted the single brick walls. The roof had an office type fibreboard suspended ceiling hanging on wires.
Because I want to insulate the floor, walls & ceiling on what is an existing room, do I have to notify the bco & adhere to the regulations?
The alternative is to just leave it as it is & i would have thought any insulation is better then none.

 

[FrankandEarl]

BRegs will definately want to play with you ... as you will be wanting them to register/sign off the alteration, whether that be "change of use" or "conversion". To get them to visit you will have to submit a quote for the work and then they charge based on a % of that. That's how you get them to visit your site -- they won't come out, otherwise.

With BRegs, the main issue will be insulation and fire/means of escape.
That means fireline plasterboard across the garage ceiling - unless you enter the void. And firelined walls adjoining .. if the firelined roof meets, and is sealed-stripped to, the wall firelining ... then you don't have to take the board up into the void - otherwise you do have to to make a near total block to fire/fume travel.

The insulation required to get the U value will leave you with little choice but Celotex/Kingspan boards...even if the roofing joists are deep.

You will be going up to a cold roof, if you haven't laid the latest insulation+ply deck thingy on the outside... and therefore you will have to allow for ventilation at the 'top' and fit a vapour barrier before pinning out the ceiling. There's also the issue of leaving some space for wiring in the void ... and not having it surrounded by/burried by insulation.
Woody has a fine point - but BCO may sit there and be doubtful about claims of a completely filled void ... especially when fitting cut boards.

If you have a single skin or a crummy double ... it's unlikely (on the wall afar from the house) that there's any cavity fill whatsoever. So BRegs will be after insulation of that, on battens.
Soas not to lose half the room to wadding, you're into Celotex again ... and you will be encouraged to make a complete "cell" of the insulation : floor-wall-ceiling.

The floor is a matter of negotiation... most likely you'll want to be floating on some small joists onto an original concrete floor. BC will want floor voids filled with insulation etc .and some sort of ventilation . That floor ventilation will have to be "clean wall" over to another outside wall ... because you cannot vent from the garage space into the habitable room , as that's a no-no for the fire/fumes (again!)

Of course - if there's any sort of direct access: garage-to-room, you're looking at a fire-door on closer ... and probably some very snooty looks from the BCO about doing that. Garage direct to habitable is always a problem.

Your escape access shouldn't be a problem ( assume the room exits to garden) bit if it's just a window...then you may have to argue for an "emergency" exit type ( low enough for a step-up)

If you have some old patio door or window ... Regs will (a) be peeved about the non-P window (b) peeved about the double-glazing of the patio door. They will be looking for big gaps and heavy glass ( 3mm + ? not sure) and that usually means a new patio with a P rating.

Basically, "bringing around" an old bit of garage conversion has more expense than you would have planned for ... but on selling the house, the Surveyor/Lawyer will be looking for the piece of paper that says it's a kosher conversion. ( If we're looking at a housing crash ... buyers can afford to be fussy on documentation)

Finally -- the wiring. These days you need to get it signed off by an approved sparks. (there's other ways of self-cert...but it doesn't really operate well) The BCO will be simply looking for the piece of paper from the sparks - don't have ? then you will not get BRegs signing off the notice. If you get a Sparks that is following the letter of the law ... he cannot sign off on a major extension re-wire, unless the rest of the house is also "safe".....nightmare

---

P.S. ... not sure about the roof ventilation. If you're re-laying boards, or even keeping original, then the boards are raised above the joists by the thickness of the batten "shim" that gives you your fall aren't they? That being so ... you have an air pathway from front to back, which can be serviced by normal facia air vents to the front and back? Wrong?


PPS - sorry about the essay. Willing to be corrected !

 

[Gilesda]

Thanks for all that info, but you've put me off doing it now, Frank&earle.
I don't mind the cost of doing the job properly, or to regs, but that creates another problem.
The amount of insulation needed for the floor would give me little headroom afterwards.
Insulating the walls to the reguired thickness would leave me with not enough room to fit everything back in.
Currently there is a drop from the kitchen door into the utility room about 5" or so. I understand this is to stop liquids in the garage being spilled under the door into the kitchen.
The previous owner (20 years ago) put a wall up across the back of the garage with a door in it, which created the utility room. there is now no drop into the garage from the utility & this would be a pig for me to rectify.
But the biggest problem is my floor standing, balanced flue central heating boiler is in the utilty & this would be almost impossible to raise up anymore then about 2".
The utility is hardly used but it is a cold room when the boiler is off & all I want to do is put an inch of celotex on the walls & floor & insulate the ceiling voids.
It looks like I'm not allowed to do that though.
Heres a crude plan of things, I don't think escape routes are a problem & the utility window is 28mm double glazed.

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[^woody^]

Lots of people do this this type of work/conversion, and most of them do it without building regs.

If you are happy and confident to do the work, and do it right then there is no problem in you doing it.

If the room is already there then you are just maintaining or improving it. The chances of anyone from the council getting involved or even wanting to get involved are minimal.

In fact I'd argue that there is no requirement to notify at all.

Do the work, do it right and thats all you need to do. Don't worry about it