Garage conversion flat cold roof issue.

[jonbhoy1972]

Hi all,

First time poster but hoping to use the forums a lot

I have helped friends with kitting out insides of extensions etc but now moving up a step from DIY'er to a garage convertor (not a bit leap but scary enough!) and am doing this for the gf who is on a very tight budget.

She has a flat cold roof above the garage which was replaced for the most part 5 years ago.Now we had Building Control in today and was gob smacked.He was not the friendliest of guys but did help in some areas but when it came to the roof its left me confused.As per the pics i have added you can see there is no vents as it is just boarded up against the house so no soffits for vent strips either side.I asked the BC about this and he just looked at it and went "Hmmmm best off getting a warm deck i reckon".I said the neighbour has the same conversion but was done 15 years back with no vents and he just said was before regs changed but then pointed out a home round the corner that had only been done 2 months back and all he could say is "Cant have been signed off then because its wrong yet plenty of same styles in the area seem to have cold roofs with no vents yet BC just say cant help! Got a builder coming to look at bricking up the door as my brickwork matching to the house is not good enough imho and will ask him but can anyone tell me what options i have ? Could i do the usual 50mm void with 150mm (100 in joists and 50 crossing them) and somehow put in roof vents because i mentioned it and he just ignored me.Luckily he said he was just filling in for the guy who would be doing my stuff in future which i am pleased about but having to break the news to the gf today has shaken her up a bit (added on top of the £1000 to move a gas meter!) . So any help would be really fantastic that i could put back to BC.Wondered if the mushroom type vents would be an option?

Thanks very much everyone in advance.

 

[^woody^]

Fill the roof void entirely with insulation, ensuring no air voids, and then fit a vapour check barrier (foil insulation, membrane or foil plasterboard) below the joists to keep moist air out. This deals with any potential internal condensationi issues.

There have been no changes to b/regs for this type of work.

 

[jonbhoy1972]

Fill the roof void entirely with insulation, ensuring no air voids, and then fit a vapour check barrier (foil insulation, membrane or foil plasterboard) below the joists to keep moist air out. This deals with any potential internal condensationi issues.

There have been no changes to b/regs for this type of work.

Hi Woody,

Asked the BC about that as i had researched it before and he said it would not be allowed .No idea why not as i am pretty sure thats what others may have done but he was pretty blunt over that suggestion as his response over and over like a broken record was if you dont have a 50mm void and ventilation then it MUST be a warm deck

Cheers for your reply.

 

[^woody^]

Fill the roof void entirely with insulation, ensuring no air voids, and then fit a vapour check barrier (foil insulation, membrane or foil plasterboard) below the joists to keep moist air out. This deals with any potential internal condensationi issues.

There have been no changes to b/regs for this type of work.

Hi Woody,

Asked the BC about that as i had researched it before and he said it would not be allowed .No idea why not as i am pretty sure thats what others may have done but he was pretty blunt over that suggestion as his response over and over like a broken record was if you dont have a 50mm void and ventilation then it MUST be a warm deck

Cheers for your reply.

The BCO is clueless then.

The whole point of a ventilated roof is to prevent condensation, in turn leading to rot. Condensation forms when warm air meets a cold surface. The fungi that causes timber rot needs a specific humidity level for it to develop.

Remove all the means for these to occur, and the roof then conforms to the various building regulation requirements.

The problem is that some building control people only know the words and pictures from the approved documents.

Ask the bloke how SIP constuction works. Ask how the principle is any different to you insulating the roof yourself.

 

[jonbhoy1972]

Well the ironic thing is even though i am no roofer and this is my first big project i have tried to do as much research as i could so i am noot totally clueless (Still everything to learn but grasping the basics) but really what you are suggesting is just a warm deck but in reverse.By that i mean you have the thick insulation sandwiched but just on a warm deck its added above with a chipboard layer yet that is acceptable! Personally i think its crazy but i am guessing it is because any small gap could cause an issue,all i know is its turned something i was looking forward to doing into a bigger money pit than first thought and may put the whole thing to bed.

 

[^woody^]

No one changes a garage conversion roof to warm or ventilated, unless perhaps the roof needs replacing in the first place. It's just insulated as above.

It's not expensive. And yes the principle is that of a thick warm deck.

 

[tony1851]

The details which the bco is pointing out are from the Approved Documents which are advisory only - ie there is no legal requirement to have a 50mm void, etc.
What matters is that the roof should be fit for purpose, including not being subject to interstitial condensation. One way of achieving this aim is to ensure that no warm moist air gets to the cold side of the insulation, so ensure you have a good, well-sealed v.c.l. underneath, and consider foil-backed board as well to be doubly sure.
But the barrier must not be punctured in any way, eg by lighting wiring.