Upstand on flat roof

[jack]

I'm renewing the felt on a flat roof of a porch which is against a irregular poll stone wall. The porch is 1.5 metres by 2.4 metres with the longest side against the wall. The original roof had a triangular wooden fillet against the wall but falling short by about 12 inches at either side, due to the lead flashing following the pointing in the stone. The lead flashing is inserted in pointing just 50mm above the roof, coming down almost to the roof level at the outer 12 inches.

I understand that when fitting new felt there shold be an upstand of at least 150mm with the capsheet.

Just wondering what the best way to fit the flashing and upstand correctly to this type of wall.

Any advice would be appreciated.

[Autolycus]

The Ruberoid "Blue Book" is the definitive guide, though it may not cover your exact circumstances

of their detailing looks very complex, but I followed it to the letter on a couple of roofs, and one has now lasted well over 30 years, and the other about 20, with no hint of problem. I reckon it's when you try to cut corners that the problems arise.

[keith_765]

The triangular strip of timber against the wall is there to help the felter to bend the felt up the wall. If its just bent at 90 degs it as a tendency to crack and not fit tight .

There are two ways of doing the up stand. Cut, chop or grid a brick joint

25mm deep x 25mm wide, 150mm above the base of the flat roof. Prime the wall and the joint with bitumen primer and just stick, with what ever you are using as a fixing, the base and the top layer up and into the joint. Point with either Leadmate or mortar.

Cut, chop or grid out a brick bed joint 25mm deep full width the brick bed joint and 150mm above base of flat roof . Prime the brick work 30mm below cut out brick joint. Stick felt up to primer line. Get a roll of code 4 x

150mm cut into 1.metre length, turn one top edge 90 degs x 25mm and insert into brick joint, continue the full length with side over laps of 100mm or 150mm. Plug with lead plugs or Bora fixing clips. Point as above. If the flat roof as to be re done again at a later date, just bend the lead apron up to reveal the felt. There is no need to take the lead apron off, using this method.

Its easier to do it than write it.sorry for any grammar mistakes

Keith

[jack]

The first full length mortar joint is 280mm above the flat roof which is also directly below a stone window ledge. The facing of the stone is also irregular, unlike a brick wall which would be flat facing. There is a mortar joint about 150mm above the flat roof, but this does not extend the full length of the roof as there are larger poll stone either side fitted into the wall. the only way that I could see this being done is to grind a slot in the face of these stones on either side to continue the joint. But i am reluctant to do this as I am wondering if it will damage the stone (cause it to split at a later date. This is why the original lead flashing had been taken across the roof in a mortar joint 50mm above the roof and had then taken a downward turn and then followed the mortar joint below the larger stones on either side. The lead thus was almost flush with the roof going into the mortar joint at the last 250mm on either side.

if it was a brick wall it would be no problem but with the irregular size of the stone blocks, it is a pain in the ass.

I have noticed that a couple of stone blocks in other places on the wall have hairline cracks through them, so I don't really want to cause any others to crack by grinting a slot in them.

Hope that you understand what i am saying and it makes sense.

Prime the brick work 30mm below

[keith_765]

This is the norm on random stone walls, just extend the joint, it should not cause cracking. If you are still concerned take the joint out on the higher stone and put a short capping strip each side over lapping by 150mm over the 150mm apron. like jump up a course at each end only.you will need wider lead for this. The joint if you decide to cut through the large stone should be done with a mortar raking disc, 4" 1/2 x 3/8th.

Keith.