Garage Flat Roof. Minimum Requirements.

[NikkiC]

Is there anywhere I can find out the minimum requirements for a pitched roof for a garage used as a workshop? The original requirements were new joists, new boards and felt. Garage area 10 square metres.

1. What type of board? WBP, OSB etc. Is OSB an acceptable substitute for WBP ply?
2. Type of felt? How many layers?
3. How should the felt be joined to the brickwork? The last time, they used white mastic and no flashing, neither was anything inserted into the brickwork.

I'm now laying down the law for these "builders" to follow. The problem is that I don't know what the law is, unless I pay a surveyor or ask a friendly roofer.... Opinions may conflict, but what would the average roofer do? By law, I'm entitled an average job!

They gave me this last time:
//www.diynot.com/forums/viewtopic.php?t=157952

(I've just changed "pitched" to "flat" in the subject title)

Nikki

 

[^woody^]

You surely mean a flat roof not a pitched roof?

Google for " Ruberoid Bluebook "

 

[NikkiC]

You surely mean a flat roof not a pitched roof?

Google for " Ruberoid Bluebook "

It's got a pitch. I can't say exactly. Perhaps 2-3 degrees?

I'll check out the book. Thanks!

Nikki

 

[^woody^]

A flat roof is up to 10 degrees

Pitched roofs generally have tiles on them

Don't confuse the two if you want to lay down the law! lol

 

[noseall]

anything below 10 degrees ain't pitched.

 

[NikkiC]

A flat roof is up to 10 degrees

Pitched roofs generally have tiles on them

Don't confuse the two if you want to lay down the law! lol

Ah, got it! Ta!

Nikki

 

[noseall]

A flat roof is up to 10 degrees

Pitched roofs generally have tiles on them

Don't confuse the two if you want to lay down the law! lol

pipped by Woodster! doh!!

 

[Xenon]

Xenon is gonna love this one!

Board needs to be exterior grade, i usually use 18mm WBP Ply.

Felt needs to be at best 2 layer HT System, or 3 layer hot bonded.

There are different ways to finish into a wall, personally i remove any copings and felt right over the wall into a felt trim. Or Termination bar as in this pic.

You can see the bar against the wall. Or lead as around the stacks in this;

Tucking felt into a chase is a bit old hat, as it won't last the 20 years that most decent felts will. Decking/felting your average garage roof should not come to more than £1400 with high quality materials.

 

[freddiemercurystwin]

http://www.fra.org.uk/hhguide/typical-details.asp but without the vapour control layer or insulation & stick to ply

 

[NikkiC]

Xenon is gonna love this one!

Board needs to be exterior grade, i usually use 18mm WBP Ply.

This is quoted from a letter I received from my bodgers (no offence to real bodgers).
"The roof ply is OSB 18mm ply. This is BBA approved. It is construction grade ply and is the preferred ply for flat roofs. WBP ply if wet on ends will delaminate. OSB ply (oriental strand bond) will not."

Tucking felt into a chase is a bit old hat, as it won't last the 20 years that most decent felts will.

Do you recommend any chasing at all? Or is it the felt into the chase you don't recommend?

Nice work. I wouldn't want to track down a leak on that roof.

Nikki

 

[NikkiC]

Hey, can you even get "OSB ply (oriental strand bond)" in this country? LOL. That was a direct copy and paste from their letter.

Nikki

 

[Xenon]

You can get exterior OSB, its £8 a board. WBP is £14 a board, which is why you're ***** roofers have used it.

Also, where they have taken the felt up the wall, this should always be done in a seperate piece of felt to allow for differential movement. I always bin copings because they are a weak spot, the whole roof is only as good as the coping. If the copings must stay, i would take them off, felt up and over the wall, then rebed the copings, this way, you have a dpc under them of the same quality as the rest of the roof.

The felt they have used is the ***** Wickes special, about £12 a roll. Premium felt is roughly £70 a roll.

While understanding a garage roof does not require the best felts, you can still put a decent Elastomeric felt on for £25-£30 a roll.

 

[Xenon]

http://www.fra.org.uk/hhguide/typical-details.asp but without the vapour control layer or insulation & stick to ply

3G Not required with HT felt as well.

Do you recommend any chasing at all? Or is it the felt into the chase you don't recommend?

Felt expands and contracts, this eventually leads to it pulling from the chase. There are enough alternatives so its not really required. Sometimes budget constraints dictate it is, but for the extra labour involved i usually fit a T bar.

http://www.areco.co.uk/shop/roofedge-trims-bars.asp

 

[NikkiC]

The felt they have used is the ***** Wickes special, about £12 a roll. Premium felt is roughly £70 a roll.

Tut. I'm going to have to stipulate that I see proof of all materials used. Receipts too. This is going to be a laugh. I should make a video of them roofing.

Thanks for that Xenon!

Nikki

 

[^woody^]

There is nothing wrong with using OSB as long as its an F2 or OSB/3 grade (load bearing and condiioned).

And IIRC, as fewer large trees become available to peel the veneer off to make ply, then OSB will become much more common as a replacement for ply

But be careful not to go overboard on the specification for a garage roof