Flat roof insulation? and EPDM to vertical wall detail?

[StephenStephen]

We have a small kitchen and bathroom extension, with a flat roof, butting up to a 2 storey building.
It's been leaking, so we plan to strip off the felt, replace any soft OSB, and re-cover with EPDM.

There's been no condensation on the ceilings of the rooms underneath, so I presume there's some insulation of some sort in there. I suspect loft rolls, which I suspect will need replacing as they will have got wet and compressed (I could be wrong about this)
There's no sign of any ventilation to the void between the plasterboard and the roof deck.
I don't know if there's a vapour barrier above the plasterboard

I'd prefer to get the whole job done fairly quickly, rather than scratching my head and ordering more materials in the middle of it.
We have quite a lot of spare loft rolls.

So I'm thinking - take the deck off and have a look at what's there:
- if it's rigid insulation then inspect, repair if needed, dry out if needed, but essentially leave it in place
- If it's loft insulation roll it'll probably need replacing, and on the basis that it worked before, go for a like-for-like replacement

With no ventilation in there, if I'm using loft roll, can I assume I can just fill the void with no air gap?
I'd appreciate any thoughts or suggestions on the insulation, thank you.

The other question is how best to finish the EPDM where it meets the vertical wall - much of it has a bellcast, so I'm thinking I can just check that it's sound, and that there's nothing bridging the underside, and leave the top edge of the EPDM stuck to the wall under the bellcast?
Where there's no bellcast, I'm wondering about grinding a narrow channel in the wall? Or put on another bellcast? I'd welcome any advice...

Thank you, much appreciated, Stephen

 

[Deluks]

How do you know that the leaking isn't condensation?

If you are replacing the insulation in a roof, you really need to upgrade it to comply with the latest billing regs. You will also need to ensure that their is at least 50% (ballpark figure) of the insulation over or under the joists.
Loft roll in a flat roof is a throwback to the 80's.

You will likely have to redo any flashing detail with the installation of the EPDM.

Go buy a decent tarpaulin for now, begin by removing a section down to the plasterboard and see what's what.

 

[^woody^]

Yes, you can do as proposed with the insulation as long as there is no condensation issue now - ie you are not altering things. Normally, if you are full-filling a roof you would have a vapour membrane at ceiling level.

For the upstand yes you can tuck the EPDM under the bell cast as long as you can get a good seal and there is no way for the wate to track back under the bell cast drip. Where there is no bellcast you can grind a slot or some suppliers just recommend sealing with a flashing tape over the EPDM.

Something like this may be more elegant along the whole lot

 

[StephenStephen]

Yes, you can do as proposed with the insulation as long as there is no condensation issue now - ie you are not altering things. Normally, if you are full-filling a roof you would have a vapour membrane at ceiling level.

For the upstand yes you can tuck the EPDM under the bell cast as long as you can get a good seal and there is no way for the wate to track back under the bell cast drip. Where there is no bellcast you can grind a slot or some suppliers just recommend sealing with a flashing tape over the EPDM.

Something like this may be more elegant along the whole lot

View attachment 388554

Brilliant, thanks, much appreciated

 

[StephenStephen]

How do you know that the leaking isn't condensation?

If you are replacing the insulation in a roof, you really need to upgrade it to comply with the latest billing regs. You will also need to ensure that their is at least 50% (ballpark figure) of the insulation over or under the joists.
Loft roll in a flat roof is a throwback to the 80's.

You will likely have to redo any flashing detail with the installation of the EPDM.

Go buy a decent tarpaulin for now, begin by removing a section down to the plasterboard and see what's what.

Thanks for your reply, I know it's not condensation because it pours in under heavy rain, and never at other times.

 

[Deluks]

Thanks for your reply, I know it's not condensation because it pours in under heavy rain, and never at other times.

Has this damaged the plasterboard, were you planning on replacing that too?

 

[StephenStephen]

Has this damaged the plasterboard, were you planning on replacing that too?

We've got away without needing to - light fittings and gaps around the edges have helped prevent pooling and sagging...

 

[StephenStephen]

Just a quick update...

Half of the roof boards are Weetabix - deep (maybe 2") still dry and very solid. No insulation or vapour membrane under these, but I think I'll put both in over the plasterboard.

The other half:
One board is chipboard - soft and saggy, which I'll replace, and the rest OSB, solid except where water has got in, so a partial replacement for those.
This half has a vapour membrane and loft roll insulation.

I found a lead skirt under all the old felt and gunk on the upstand, so that's a relief.

A lot of the fall is generated by variable depths of gunky black stuff, so I guess I'll take all the boards off and put in firring strips.