Building over flat roof

[23vc]

When building a first floor extension on existing walls which previously had a flat roof, are there any clever ways of keeping the existing ceilings (underside of flat roof) intact and dry? Considering buying a place where I’d want to do this, but would take me weeks and weeks to do the brickwork before getting top roof on. I can’t really think of a decent way of keeping the rooms below dry without a lot of faff. Was thinking those water resistant caber boards and a lash up of lapped dpm and miss a brick out for water to drain back out. It’s a fairly big area (full width of back of house) so can’t just throw a tarp over it very easily.

I assume people tend to just get the brickwork up quick with an eye on the weather. This one includes a gable build up too which adds to the time it’d take.

 

[stuart45]

A temp roof combined with the scaff is the standard method. You need a scaff anyway so having a tin hat is the normal way. Trying other methods might lead to a lot of water coming in if the water can find a route in somewhere, which it often does.

 

[23vc]

Thanks, guess id just suck up the cost of the tin hat. It’s not a massive area.

I’m also thinking timber frame inner and brick outer could be an option. I could timber frame straight up off the existing flat roof joists possibly. Then get that up quick with membrane and rafters. Then do the outer skin.

 

[stuart45]

You would have been OK this summer. I took a chance when extending a flat roof extension and topping the lot with a pitched roof, but it only meant cutting the edges of the deck so I could get the rafters in. Once I had a few in I could tarp it.

 

[^woody^]

Once the inner leaf is a block course or so above the flat roof, you can use a decent tarpaulin or DPM fitted around the four walls and angled to an opening left in the wall.

You would use a sheet big enough so that it is one piece when formed going through the wall and draped into a temporary rainwater hopper and down pipe, so that the outfall does not saturate the wall below.