Garden Room Flat Roof in EPDM

[efunc]

Hi all,

I posted a thread about my garden room in the 'Building' section of the forum, but many of my questions relate to my roof problems, so I thought I'm better off posting those here.

I've had a garden room half built and have had to send the builders packing after a poor job. Now I'm trying to see what can be done about it to make it useable. The roof is a flat roof which was supposed to be done in EPDM, but they arrived with narrow rolls of Cortex EPDM membrane which they stuck down but have left lots of loose seams and leaks around the flashing where it's not even bonded down. The roof is about 6m wide and 3m deep.

I think the pitch is something like a 3cm fall to the front along most of its width, but at the left corner is actually pitches to the back and side a little bit. The red arrows indicate what I think it’s doing, but mostly it’s more or less flat.

I’ve been considering various options for improving things, which will mainly mean re-doing the flashing (with something like this) and sealing the whole surface, but might include increasing the pitch.

- To entirely redo the surface in EPDM I would need to remove the existing EPDM membrane back to the OSB/3, or overboard the EPDM without removing it. Overboarding with OSB would be difficult for me, but also add far more weight to the structure than I want. In order to install wedges and raise the pitch though I would need good strong boards, like 18mm. If I don’t change the pitch though perhaps an alternative is just overboarding with lightweight 4mm WBP Ply External Plywood. 6 boards would only weight about 42kg as opposed to almost 200kg of 18mm. Not to mention the new EPDM which may be another 50kg. 4mm might warp and lift too easily though. Should I be concerned about this, or just go for it? Alternatively is 12mm likely to be adequate, or maybe 8 or 10mm, given that these are just going to be sitting on existing 18mm boards? Strength isn’t an issue because it would just be screwed right on top of the existing surface, and then another EPDM sheet stuck on this.

- I could also try ripping up the EPDM and replacing it with a proper one without overboarding, but that could be long and messy. It would also no doubt leave a lot of thick mastic behind and I'm told a roofer would not want work with the surface like that. It would still need to be overboarded. Is that correct?

- Another alternative a colleague suggested was just sealing the existing EPDM properly and then overlaying it with lightweight Polycarbonate boards to create an additional layer. I might even be able to investigate lifting it higher at the back using spacers or batons to improve the pitch, but obviously the structure won’t be strong enough to stand on, (not that this will matter)

- I guess corrugated PVC board could be used as well as it’s cheap. None of this will be seen from the ground as it’ll hidden behind the fascia and guttering that it’ll overhang into I guess.

Any advice or suggestions?

Thanks!

 

[Notch7]

I would pull off the cortex epdm, unscrew decking boards, sort out firrings to create fall to front of about 1 in 40.

Put back deck boards and cover in epdm.

You can put up some plastic for temporary protection in between work.

https://www.screwfix.com/p/capital-valley-plastics-ltd-damp-proof-membrane-black-1200ga-4-x-3m/73066

 

[efunc]

Thanks for the advice. Yes, that would be the sensible thing to do. When I took a look though I found the OSB was nailed on hard, as well as screwed on in places. I have visions of it being a real struggle to get these up, but yes, removing them and simply turning them over would be ideal.

if not though, what's the minimum weight of ply or osb I could get away with to overboard?

 

[StephenStephen]

EPDM will stick to itself if you use contact adhesive (which you can get from an EPDM supplier) - if you trust that the existing EPDM is actually stuck down.
I'm wondering if it's possible to cut through the fixings holding the OSB down in the corner, adjust the fall in the corner where it's going the wrong way, then refix, and use contact adhesive to put a new single piece of EPDM over the top? I'm not an expert, just an amateur thinking aloud here.

 

[efunc]

EPDM will stick to itself if you use contact adhesive (which you can get from an EPDM supplier) - if you trust that the existing EPDM is actually stuck down.
I'm wondering if it's possible to cut through the fixings holding the OSB down in the corner, adjust the fall in the corner where it's going the wrong way, then refix, and use contact adhesive to put a new single piece of EPDM over the top? I'm not an expert, just an amateur thinking aloud here.

Thanks Stephen, all the suppliers I spoke to advised against gluing epdm to itself, but I agree, it sounds plausible with a contact adhesive. Using that much contact adhesive would be expensive and difficult, but I'm trying to salvage something that could otherwise be doomed. However some of the existing epdm isn't properly bonded down yet, so I would fist have to either stick it down, or remove it entirely.

I could also potentially overboard just that right rear corner to improve the fall, as that wouldn't add an enormous amount of extra weight.

 

[efunc]

a couple of quick fire questions as my re-roofing investigations continue:

Has anyone encountered high-density fibreboard for roofing? I came across it on youtube, but it may be an american thing. It is used as a recover board over existing roof decks prior to reproofing, and as a protective cover over insulation. Available in 1/2-inch and 1-inch high-density thicknesses. I’m not sure of its weight or strength but it may be the preferred solution to 18mm OSB.

Secondly, what can I do with the fascia? I was thinking it need battens over membrane first, before cladding with T&G Larchwood siding, BEFORE thinking about bringing the EPDM sheet over and pinning it with the drip trim. However, is it possible to forego that completely and just use a UPVC fascia trim secured directly to the OSB before hemming over the EPDM and using a drip trim on top?

This is an example of it, but there are many versions, but all in the US as far as I can tell. Celotex Structodek is a common brand over there. It’s about 22lbs for a 1/2” 4’x8’, so in total my deck would weigh about another 50kg, which is ok as a compromise. Anyone know if this sounds like a solution and if it’s available in the UK?

 

[efunc]

Having spent the entire day researching this and coming up against dead ends I'm of the opinion now that 9mm ply is the lightest material I could get away with overboarding, but is still almost 100kg. This is option number 2.

Option number 1 is now to remove the existing EPDM and see how far I get, and perhaps use something like this firestone cleaner, however that only comes in 500ml aerosol. Anyone know if heatgun and meths, acetone or white spirits might be a cheaper alternative? Option 3 is to leave it as it is and put polycarbonate sheeting over the top, raised a little at the back using spacers and flashed against the rear wall falling to a gutter at the front. Anyone have any thoughts one how to proceed?

 

[efunc]

Anyone have any thoughts about the clean up methods I suggested for removing the EPDM?

Secondly, someone just offered to do a single layer heavy duty sbs torch on including drip edging, for a very good price if I remove the EPDM. Aside from the fact I don't know him from adam and he only advertises on gumtree, is this a plausible solution? I thought torch-on often requires two or even three layers to properly protect, particularly is there are a lot of seams. If the roof is 3m x 6m is that usually something that can be done in one sheet of torch on? This is crucial to me as the roof is dead flat and I don't want any seams or joins at all. Anyone?

EDIT: SBS seems to come in 1m rolls, so there would be plenty of overlapping seams. I'd imagine a base layer or two and capping layer would be prefered. Is single layer 'heavy duty' (whatever that means) even a thing? Anyone any experience of this?

 

[vinty]

Normally you can get EPDM made to measure, measure the length and breadth of the roof and add on a bit all round to cover drips and upstands at flashings.
I did a Firestone EPDM contractors course years ago in Cheshire.
Firestone claim they invented EPDM and have sold over 1billion sqm's world wide,
It comes in rolls 50m longx9m wide ,if you give the the dimensions of your roof they simply cut it to fit just like a carpet.
On a new deck you use a white water based adhesive to stick the membrane down ,any wrinkles or blister's you brush out with a brush, the edge drips and upstands are stuck with contact adhesives ,metal or pvc edge trim is then screwed on ,and can be sealed with a 3inchFirestone seam tape .

 

[vinty]

Anyone have any thoughts about the clean up methods I suggested for removing the EPDM?

Secondly, someone just offered to do a single layer heavy duty sbs torch on including drip edging, for a very good price if I remove the EPDM. Aside from the fact I don't know him from adam and he only advertises on gumtree, is this a plausible solution? I thought torch-on often requires two or even three layers to properly protect, particularly is there are a lot of seams. If the roof is 3m x 6m is that usually something that can be done in one sheet of torch on? This is crucial to me as the roof is dead flat and I don't want any seams or joins at all. Anyone?

EDIT: SBS seems to come in 1m rolls, so there would be plenty of overlapping seams. I'd imagine a base layer or two and capping layer would be prefered. Is single layer 'heavy duty' (whatever that means) even a thing? Anyone any experience of this?

You would need 3 layers a nailed on layer and 2 layers of torch on felt, 2mill under lay and 4mill cap sheet .
If the felt top layer is plain black in colour you would then have to paint it with Aluminium solar reflective paint.
A better option is probably take the old membrane and have redone in EPDM properly.

 

[efunc]

You would need 3 layers a nailed on layer and 2 layers of torch on felt, 2mill under lay and 4mill cap sheet .
If the felt top layer is plain black in colour you would then have to paint it with Aluminium solar reflective paint.
A better option is probably take the old membrane and have redone in EPDM properly.

Thank you, that confirms what I suspected. Someone did say they could do a single layer of SBS Torch-on for £540, but that sounds like a total bodge job. If, on the other hand, the base layer were nailed on over the top of my current EPDM and another 2 done on top I would be quite interested in this as it would save me having to rip up the EPDM or over board it! Is that how it works if I do it properly? Also any idea of the approx weight per m2 if I do a 3 layer torch-on? It sounds like it could get heavy; much more so than EPDM anyway.

 

[efunc]

Normally you can get EPDM made to measure, measure the length and breadth of the roof and add on a bit all round to cover drips and upstands at flashings.
I did a Firestone EPDM contractors course years ago in Cheshire.
Firestone claim they invented EPDM and have sold over 1billion sqm's world wide,
It comes in rolls 50m longx9m wide ,if you give the the dimensions of your roof they simply cut it to fit just like a carpet.
On a new deck you use a white water based adhesive to stick the membrane down ,any wrinkles or blister's you brush out with a brush, the edge drips and upstands are stuck with contact adhesives ,metal or pvc edge trim is then screwed on ,and can be sealed with a 3inchFirestone seam tape .

Yes, I've had a quote for doing it in Firestone EPDM, which is my fallback position. When you did the course did they train you in techniques to secure it mechanically at all, as an alternative to bonding down? I know it's an option because I've seen it mentioned in passing but can find no info ot it and in what circumstances it can work. I presume it's bonded and pinned in at the edges using trim, but just guessing.

 

[efunc]

Just got a reply from a big US roofing firm in response to my question above regarding EPDM:

"EPDM can be installed as a mechanically attached, fully adhered, wind vented or a ballasted system. Mechanical attachment is the easiest and usually the most cost effective option."

Anyone know how this works, where I can find info on it, or who does it in the UK?

 

[efunc]

OK, I think I understand the mechanically attached system now. This Firestone video explains it. Basically it's laid on (seemingly in panels rather than single sheet) and then held down with battens screwed over the top. However it looks pretty labour intensive to me, and I'm not sure of anyone over here that uses this technique:

And then there's this other Firestone video that shows a system being bonded directly on top of insulation panels using a spray on contact adhesive or something! This would also be a solution for me enabling me to cover my existing EPDM roof without removing it all:

If anyone know of a company in the UK doing this please let me know. Everyone I've spoken to so far insists I have to over-board with 18mm OSB.

 

[vinty]

You would be better stripping of the existing membrane,and recovering it with a single sheet ,you could do it in less than a day.
Mechanical fixing is usually for large industrial roofs.the reason panels are used is because the sheets of EPDM have maximum width they then have to be joined with seam tapes.
A ballasted roof needs to a 50mm layer of roofing Peebles which puts a lot of extra weight on the roof.
If your roof is only 6mx3m you should have no problem getting a single sheet cut which means no possibility of leaking seams.
We used to do quite a lot of Firestone roofs years ago.
Firestones had a technical department with a bloke whose job it was to answer customers queries about fitting Firestone, his name was Carl Bailey ,you just had to phone him up and he would keep you right ,I don't know if he is still there.
Firestones used to have a list of approved Firestone contractors from all over the country.