Warm Roof To High

[GrantMcscott]

Hi

I need to do a warm roof for my porch either EPDM of GRP the issue I have is the spec is for 170mm thick insulation on top of the OSB.  If I do this the flashing will be above the weep holes for the lintel and very close to the windows and look silly.

 

Is it possible to put 40mm of insulation on top and 15mm in the joist zone will this be OK or will I still get condensation?

 

does the flashing need to be chased into the mortar or can I chase out the block

 

thanks in advanced.

 

 

[Mr Punter]

If the porch is not wider than the window above, you don't really need to worry about weep holes as there is not enough blockwork to cause an issue.

[Temp]

Opinions differ but some say you can put insulation above and between on a warm roof provided you get a condensation risk analysis done. As I recall the rule of thumb is no more than 1/3rd of the insulation between the rafters, the rest above.  So if the spec is 170mm you might be able to change that to say 60mm between the rafters and 120mm above. 

 

The alternative is to switch to a ventilated cold roof and put all the insulation between the rafters. On a porch it might be better to run the rafters side to side so you can have vents under the eaves both sides. If you run them front to back you really should have vents at the front and back where the flashing will be. That is possible but complicates the flashing.

 

I guess you can't reduce ceiling height?

Edited August 30, 2022 by Temp

[GrantMcscott]

9 hours ago, Temp said:

The alternative is to switch to a ventilated cold roof and put all the insulation between the rafters. On a porch it might be better to run the rafters side to side so you can have vents under the eaves both sides. If you run them front to back you really should have vents at the front and back where the flashing will be. That is possible but complicates the flashing.

 

I guess you can't reduce ceiling height?

Hi The rafters are already in and they run front to back 😞

 

The ceiling is already as low as it goes.  I have 225mm from the OSB so the time I put slope on the roof and insulation ect then it is above the block mortar line so I need to go upto the next block for the flashing and will look daft

[GrantMcscott]

16 hours ago, Mr Punter said:

If the porch is not wider than the window above, you don't really need to worry about weep holes as there is not enough blockwork to cause an issue.

Hi the lintel is 2.6m wide