EPDM Roof - Damp Substrate

[Davieboy84]

Hello all,

 

I'm currently in the process of building a garden room which is 4.8 x 3.6m. The plan was for the sips kit to arrive in August to give me some nice sunny weather to build it and get the EPDM roof on. The kit was delayed however and didn't arrive until the middle of November, which meant I only had a 3 day dry window to erect the kit before the rain came in (I live in Scotland, it's been a very wet winter). I used a DPM secured over the sides with battens to protect the roof over winter and it's performed pretty well, allowing me to crack on with the bifold, window and cladding.

 

My plan was to wait until warmer weather in April or May before fitting the EPDM roof, however today I've noticed a small drip inside the garden room coming from the roof. I climbed up and had a look at the DPM and can't see any obvious tears, however it might just be starting to fail slightly after quite a harsh winter.

 

My question, is how dry does the substrate need to be when installing an EPDM roof covering? I'm certain that a majority of the roof timber is none dry, apart from this one small section where there is a drip. 

 

Do I need to wait for a week long spell of dry weather (quite rare in Scotland . . ) with the DPM removed to completely dry out the roof timber and sips panels, or will a day of dry weather do the trick? 

 

I'm now quite keen to get the proper roof covering on but I want to make sure it's done correctly. Thanks in advance. 

[joe90]

4 minutes ago, Davieboy84 said:

however it might just be starting to fail slightly after quite a harsh winter.

It should never fail in that short time (unless split/torn because of movement/wind). 

[Nick Thomas]

32 minutes ago, Davieboy84 said:

My question, is how dry does the substrate need to be when installing an EPDM roof covering? I'm certain that a majority of the roof timber is none dry, apart from this one small section where there is a drip. 

 

The roof deck needs to be dry. Two reasons for that -

 

First, any water up there will be pretty much trapped once the EPDM is on.

 

Second, the glue - certainly for the kit I used, it was water-based for most of the roof, with something stronger for the edges. The water-based stuff will definitely fail if the base is wet-wet - it just won't stick.

 

What I ended up doing was flipping the OSB sheets that made up my roof deck over, so the wet face was pointing down and the dry face up. Might not be an option for you.

Edited February 23 by Nick Thomas

[jamiehamy]

Is the roof SIP? If so, the moisture could be coming from there is it hadn't been stored right at any point. It's not unheard of.

 

You do need a bone dry substrate for EPDM, I wouldn't be happy with a single day, but in April/May we do get nice long dry spells - if you get clear skies for 3 days that should dry the surfaces you need to bond to.

[Nick Thomas]

If most of the roof is dry and there's just a small wet spot, you might get away with it, or that bit might spread out significantly, then bubble up and annoy you every time you see it

 

I was out today with a heat gun drying out some bits of wall... depending on the size of your wet patch, and the general inflammability of your build, this might be a good idea, or might not. In my case it was definitely "pushing your luck mate" territory.

 

My backup plan if the EPDM didn't stick well, or got horribly creased or something, was to slap a green roof on top to hold it in place. Your joists would need to be sized appropriately though.

Edited February 23 by Nick Thomas

[Davieboy84]

30 minutes ago, jamiehamy said:

Is the roof SIP? If so, the moisture could be coming from there is it hadn't been stored right at any point. It's not unheard of.

 

You do need a bone dry substrate for EPDM, I wouldn't be happy with a single day, but in April/May we do get nice long dry spells - if you get clear skies for 3 days that should dry the surfaces you need to bond to.

Yeah it's a SIP roof. Thing is, it's been bone dry for 2 months, however I noticed this afternoon that one of the battens holding it down at the side was loose. There has perhaps been some driving moisture getting between the DPM and room. 

 

I've reset the batten and the drips have stopped. Hopefully it dries out fully over the next few weeks and when I get a dry spell I'll get the DPM stripped and let it air for a few days before getting the EPDM on. I'll also get a heat gun in case there are some small areas that need some specialist attention. 

 

I'm not massively fussed over how it looks, I'll never see it. I just want it to perform well over the next 15/20 years.

 

Thanks for all your responses