Hi, I'm ready to build my flat roof with Lantern. The plan is to do a 'Warm Roof', the extension Is on a Bungalow so the brick and blockwork are at Wall Plate level. The extension is approx. 6m X 3m, a small utility room and cloakroom at one end and the rest being a dining room.
I have had a suggestion that would cut down on an excessively deep Fascia board, that is to bed the rafters directly onto the blockwork( packed to compensate for the missing wall plate and use blockwork in between the rafters and then add, say, 3 more courses of bricks on the outer leaf, continue the insulation through to the top of the rafters, then deck the top, then 125mm Insulation then a second deck before final sealing membrane.
There will be a roof lantern approx. 2.5m x 1.25m over the dining area.
Question 1. Does the methodology sound good?
Question 2. How many rainwater outlets on the roof would be recommended?
Question 3. There is an existing door and window in the original building, these will be removed along with the external leak brickwork (that would be in the dining area), it has a 7" x 21/2" timber lintel. I think this will need replacing for the additional load of the new roof. What would be the advised replacement ( Steel U/C, Catnic o Concrete) the internal blockwork span is 2.185m.
Thanks in advance for any advice given.
Barry
Are you a tradesperson and able to answer this question?
Hi Barry,
I see what you are trying to achieve but by installing your rafters directly onto your blockwork directly and blocking them in could give you a structural problem later down the line when the blocks around loaded joists will open at joints local to the joist causing you to have internal cracks, warps and possible effect your ceiling lines if the block directly under the rafter fails and the joist sinks a bit.
When Rafters are on a wall plate it spreads the load evenly over the masonry to reduce the risk of damage to the masonry as do wall hangers.
I think it would be worthwhile speaking with your Structural engineer or Architect before you proceed with any further.
I hope this helps
Good luck with your project
Chris
Answered31 July 2019
24
Anonymous user
We do this work a lot - Using a warm deck system does give you oversized facias and it looks ugly .
The drop down method inside then uplift on the outer skin with extra courses is
a very expensive method and labour intensive in my opinion
We have been using a hybrid roof system fully ventilated and have had no issues with building control
So standard build with wall plate - Joists - VENTILATED Soffit and facia boards
If you set your fearing out to allow for water to fall all around the atrium this will also help with the cross ventilation all round alternatively counter battons
150 solid insulation between the joists - 50mm to underside with plasterboard .
(Celotex or Recticel)
Also insulated the kerb with 25mm and plasterboard .
Answered11 August 2019
0
Anonymous user
As I am not a builder I cant fully visualise your description!
However I would recommend a wall plat( say 2x4 wall plate.)
I would also say you need 2 nox3" outlets.
Hope this helps.
Aidan quinn
Hi barry
This is common practice for me on extensions.
You can still fit the timber wall plate and install your roof. We then run usually another three courses of bricks on the outside. Then you get normal size facias, you can put insulation in between joists upright so cavity is still there.
One rainwater outlet if you're using a new soakaway to b. C regs.
The best thing to use at opening would be a catnic lintel, with dpc over the top and two weelholes one at either end.
Please message me if you require any further assistance.
Kind regards
Gary
