Garage Flat Roof Replacement - General Process?

[garuff]

Hi,

I'm handy enough about the house to feel this is within my capabilities, but I'm not au fait with various aspects of roofing... excuses out of the way, I'd welcome any thoughts/opinions on the below

2850 x 5550 detached single garage, single skin brickwork - currently has a (presumed asbestos) cement roof, which is c.3.5 sheets wide by 2 sheets long. Roof leaks, ivy has overrun the sides and it seems to have condensation issues too.

Slopes from front to back, front is about five bricks higher than the back (forgot to measure the actual height differential).

Getting rid of the existing panels should be fine (brother works in hazardous waste disposal). Looking to replace with an EPDM covering.

So, some questions:

• The slope of the roof is achieved through roughly cut bricks and mortar. No wall plate (?) to speak of -- for the new roof I think I'm going to need to add more joists for strength (bring it to 400mm centres), how would I actually secure these to the same height/angle as the existing joists?
  
  Without a wall plate (I don't know if that's the right term! Bit of wood running along the top of the brickwork) where/how would I affix fascia for securing the EPDM?
  
  Would you fix the new joints on an angle to match the fall of the roof? Or have the joist square and firring strips (?) to create the angle on the top of the joists?

Alternatively if I'm barking up the wrong tree and someone wants to point me in the right direction, go for it (not that anyone would hold back anyway )

Thanks!

 

[noseall]

Remove sloping cut bricks until you have a level course all around.

Add more brick courses if necessary.

Bed and level tanolised 100mm x 75mm wall plate all around.

Fix 175mm x 50mm joists at 400mm centres (narrow ways) to wall plate.

Strap wall plate to brickwork with 1m bent straps.

Add centre bridging to joists.

Fix firring strips or add decreasing increments of timber packers to joists to create falls (depending upon direction of fall).

Fix 18mm CDX ply sheets to joists.

Fix fascia cradling (plastic clad) or fix timber fascia.

Fix angle fillet (cocking fillet) and gutter batten (drip) where necessary.

Fit membrane.

 

[garuff]

Hi Noseall,

Thanks for the extensive list - has helped me start to get my head around a few things. As would be expected, has thrown up a few questions if you wouldn't mind having a look

Bed and level tanolised 100mm x 75mm wall plate all around.

Bed this into Mortar?

Fix 175mm x 50mm joists at 400mm centres (narrow ways) to wall plate.

Would you recommend to fix the joists onto the wall plate or hang them off it?

Add centre bridging to joists.

Just to check... as in a run or two of joists cut down and secured perpendicular to the joists? How would you attach these?

Fix firring strips or add decreasing increments of timber packers to joists to create falls (depending upon direction of fall).

I think if the roof has been 'flattened' so the fall can be any direction, I'd have it falling towards the long edge ('into' my garden) so need firring for about 3m

 

[noseall]

Bed the wall plate on mortar. Don't be alarmed if it does detach from the bedding mortar once everything dries. This is normal. Just re-position the plate back in its original place. You can secure the plate with the bent straps but we tend not to fix these until after the joists have been fixed, for fear of clashing.

Fix the joists to the plate. You can either skew fix them or use angle plates.

Central bridging sits (snug) between the joists, i.e. just use the off cuts (if applicable) from the joists.

Falling the roof the short distance makes sense. Firring strips it is!