Upstands for garage felt roof

[mmchutchon]

I'm planning on overlaying my garage roof tomorrow (weather permitting) with three layer torch-on felt. My primary question is about the upstands.

There are 2 or 3 courses of brickwork around the back and one side of the roof. The previous felt upstands passed right through the brickwork with the top course laid on top.

One quote I had suggested fixing 50 x 100 mm tanalised timber to the top of the walls and forming the upstands over the timber. That sounds a better option but exactly how would I form the upstands? Bring the top two layers over the timber and say 150 mm down the other side, torching all the way? It's an external / boundary wall so this is possible.

Also, I presume this is the way to do the work: -
Pierce existing blisters, flatten existing felt as best I can
Remove existing upstands.
Tidy existing brickwork and fix timber on top.
Sweep existing roof clean of debris
Cover with bitumen primer.
Loose lay ventilating underlay with no overlap following fall of roof.
Torch on middle layer across fall of roof starting at bottom.
Torch on top layer as per middle layer.

Any other handy hints? Seems frustratingly difficult to get a good 'how-to' guide on felt roofing!

Thanks,

Mark

 

[alan333]

The correct way to do your job would be...

Strip and remove all old felts down to roof boarding.
Repair/renew boarding and brickwork as necessary.
Fit timber (plywood or similar) cap to the top of your brickwork, and fix tile batten or simlar to the outer top edge.
Apply primer to bare brickwork on upstands.
If you have tongue and groove boarding then nail a first layer at 6" centres.
If you have plywood or chipboard then torch 4" strips onto all the board joints instead.
Torch first layer, starting at bottom of flow. Also torch edge flashings up the upstands and down over your tile batten.
Fit "welted drips" to your lowest edge/drain edge. This stops moisture "creeping back".
Torch top layer but don't overlap at the same places as your first layer, stagger it.
Torch edge flashings (if necessary) and welted drips to upstand edges.

Attatched is a crude drawing in cross section. The black line is what felts I suspect currently exist. The brown squares at the top are where to put your new timber. The thin black lines are where your screw/nail fixes should go. The blue lines are what your first torched layer should look like, and the green lines are what your top layer should look like, including the welted drip detail. Note the welted drips are nailed into the tile batten good side facing inwards, then torched back on themselves such that the good side now faces outwards.


If you plan to overlay on existing then your plan is ok but...

Only do so if the existing is fairly sound, and there is no moisture trapped within it.
Burn the surface of the old felt until the bitumen shows through, and you can then skip the primer if you like.
Skip the vented layer altogether.
There's no rule on laying the felt across the roof. Sometimes the overlaps can create a small "dam".
Make all side laps a minimum of 2", and all end laps and upstands a minimum of 4".
Ensure enough heat is applied such that there's a good adhesion rate/bitumen flow at all laps.
Hint - loose fitting rubber gloves are best so you can throw them off easily when you torch them.
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[Xenon]

Top advice from Glasgow, i'd give the man a job. I'd just fit a GRP trim instead of a drip though.

 

[mmchutchon]

Just a quick note to say thanks for the fantastic advice. Bought all my kit Saturday morning, started tidying the old felt and it just started coming away so ripped all of it off, back to the decking and brick.

Got vented base layer and middle layer on now, all the timber is on top of the walls for the upstands awaiting the middle layer of felt. Will buy my capping sheet today and hopefully have it all sorted end of tomorrow evening (so glad the weather looks like holding!)

Thanks again,

Mark