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Roofing questions for the brave!


Pocster

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15 minutes ago, Oz07 said:

To be fair this scenario is still cold roof as far as venting is concerned isn't it. I.e. The insulation will be between and below rafters meaning you will need ventilation to stop condensation on timbers. A true warm roof would have insulation above rafters and no condensation risk.

 

thats my understanding anyway...

Yes. Mine is a true warm roof. 195mm rafters fully filled with insulation, no gaps. 100mm wood fibre board over the rafters acting as the sarking board and extra insulation. Breathable membrane over that, no gaps anywhere, lapped over the ridge. Counter battens down following the rafters, then horizontal tile battens over that, the counter battens ensure a gap under the tile battens.  Dry vented ridge and eaves vents ensure the gap between the membrane and the tiles is ventilated.

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43 minutes ago, PeterW said:

Ok so he's gone Rolls Royce but hey ...

 

This is what you need to read, specifically the section on roof construction. 

 

If it's a warm roof to the ridge i.e. Insulation all the way within the rafters, then no ventilation is needed. Cold roof i.e. Insulation at ceiling level, then you need ventilation. 

 

http://www.proctorgroup.com/images/downloads/Condensation-Control/Roofshield/BBA/Roofshield - Warm Roof BBA (96-3220 i8).pdf

 

 

 

24 minutes ago, Oz07 said:

To be fair this scenario is still cold roof as far as venting is concerned isn't it. I.e. The insulation will be between and below rafters meaning you will need ventilation to stop condensation on timbers. A true warm roof would have insulation above rafters and no condensation risk.

 

thats my understanding anyway...

 

Yeah. This is my confusion. 

So it's like some kind of hybrid. I *assume* it's treated as a cold roof for ventilation purposes . 

 

But you could argue the membrane could overlap the ridge because it's breathable ........... ?????? 

 

Edited by pocster
confusion master!
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So the definitive answer on this should be the BS5250 recommendation. 

 

This is the detail on roof construction where there is either a small void above or no void above the insulation. 

 

IMG_0639.thumb.PNG.109c59459b0d37085432f394fd928bca.PNG

 

IMG_0638.PNG.1b835d2cc761f641e64c52e8fbd58bc3.PNG

 

if following either of these the key is that there is a fully sealed VCL below the insulation and no ventilation required if using a full breather membrane. 

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1 hour ago, PeterW said:

So the definitive answer on this should be the BS5250 recommendation. 

 

This is the detail on roof construction where there is either a small void above or no void above the insulation. 

 

IMG_0639.thumb.PNG.109c59459b0d37085432f394fd928bca.PNG

 

IMG_0638.PNG.1b835d2cc761f641e64c52e8fbd58bc3.PNG

 

if following either of these the key is that there is a fully sealed VCL below the insulation and no ventilation required if using a full breather membrane. 

 

Ok!

 

So for me then ^_^; I can overlap my membrane across the ridge because it's breathable. Was going to VCL the PIR underneath anyway. Lol!; wonder what my architect will say O.o

 

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Architect can spec what he wants ..!! Building Control will only sign off what is correct so they are the ones to consult. 

 

If you say you are building it to the detail as shown in BS5250 as per the BBA certificate for the product then you can't exactly go wrong ..!!! 

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2 minutes ago, PeterW said:

Architect can spec what he wants ..!! Building Control will only sign off what is correct so they are the ones to consult. 

 

If you say you are building it to the detail as shown in BS5250 as per the BBA certificate for the product then you can't exactly go wrong ..!!! 

LOL!

 

You think BCO will even look?; trust me he won't!. But yes following that spec seems the way to go!. Get ready for photo's! B|

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@pocster

@PeterW

I think there may be a misunderstanding here on what the British Standard is recommending. When it refers to "air-open" and "tight" coverings it is referring to the final roof finish - IE are you using a "tight" fitting interlocking roof tile or an "air open" loose fitting slate.

 

In my view If you have tight fitting interlocking roof tiles in the scenario that you've described then you do need batten space ventilation. I know your architect has specifed a tightly sealed VCL on the warm side of the roof as well as a very high quality LR underlay however its still possible to get situations where you get condensation on the underside of the roof tiles - IE in warm humid summer weather - when you get a sudden drop in temperature such as during a thunderstorm you get sudden cooling of the roof tiles with condensation occurring within the roof void. In a situation where you have tight fitting roof tiles its best to have a ventilation gap to allow this condensation to rapidly evaporate.

 

Ian

 

 

Edited by Ian
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Right!

 

I've just done the drip tray verge things :-)

Mine weren't like the video all nice and interlocking!

I've overlapped them and even added a batton where I 'feel' they might sag.

I assume this all looks ok?

The gutter clip is attached to a piece of wood to simulate the fascia thickness.

 

Am I ready for the first membrane roll out and the first 2 battons ?? :o

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Edited by pocster
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2 minutes ago, pocster said:

Barney12 you are in my will!!

 

But!; is it correct??????????????????????????

 

Well I'm no roofer but it looks the same as mine did! But I didn't bother with the fancy battens :) 

Edited by Barney12
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1 minute ago, Barney12 said:

 

Well I'm no roofer but it looks the same as mine did! But I didn't bother with the fancy battens :) 

LOL!

 

That's good enough for me!

Stay tuned for the next stage of exciting photo's named "how to tile a roof without a clue" xD

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20 minutes ago, PeterW said:

Leave the plastic on the fascia until the last minute. Then just bung the gutter on. 

 

Don't forget if you use high capacity gutter you don't need a fall either so you can make it look tidy. 

Sure thing ; still thinking about adding it last though even if it's a bit trickier 

not sure how it marries up on the edges ; so was leaving for another day 

suppose I could put it on and let it overhang and cut later if need be 

Edited by pocster
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1 hour ago, pocster said:

LOL!

 

That's good enough for me!

Stay tuned for the next stage of exciting photo's named "how to tile a roof without a clue" xD

 

We could start a "Without A Clue" series, mine being bathrooms! :)

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I decided after some thought that you guys were right ^_^ ; so I put the fascia on first.

 

All looks ok. Just wondering where fascia straight run meets fascia straight run do you buy some crappy plastic to cover the join or is it just me being extra fussy.

A multitude of exciting photo's attached!! (photo 2 of the exciting bit where fascia meets fascia!)

 

 

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27 minutes ago, PeterW said:

You buy joint covers ...

 

leave a 5mm gap between each piece and then superglue it to ONE SIDE ONLY so it can move with ExpAnsion when it gets warm

Ok ; I got a 1mm gap :-)

also a "builder" told me the ridge tiles and hip tiles are different . This right ? ; I seem just have 1 type ....

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Definitely take heed of the "only superglue the joint covers on one side" tip and very definitely leave an expansion gap, as uPVC expands like crazy when it gets warm, and black uPVC will get very warm in sunshine.

 

Our fascias are fine, as the roofers fitted them properly, but around a part of the uPVC fascia that I used at the base of our larch cladding we have one split joint plus a big bow in one section, where the expansion forced it off the underlying battens.  The guys that fitted it didn't leave either a big enough expansion gap or only glue the trim on one side.............

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