Possible shed roof leak

[AdamD]

Went to the shed for the first time in a while yesterday and noticed wet handlebars on my bike so looked up to find quite a wet interior roof, however only about 1/4 of the shed nearest the door and rest is all dry. Roof has the usual felt and it looks to be in good condition so I’m a little bit stumped. It is concerning as it does feel very wet. Also the fascia above the door is very moist whereas the otherwise is dry, making me think that water has somehow got underneath the felt and is seeping down. A couple of pictures attached.

 

Any advice as to fault finding before I go the whole hog and remove the felt?

[markc]

I would hazard a guess at high winds plus rain pushing the water up under a felt lap/joint

[AdamD]

33 minutes ago, markc said:

I would hazard a guess at high winds plus rain pushing the water up under a felt lap/joint

Makes sense given the horrendous weather we’ve had over the last few months. Do you think it’s worth removing the felt from that side and re-applying some new?

[markc]

3 minutes ago, AdamD said:

Makes sense given the horrendous weather we’ve had over the last few months. Do you think it’s worth removing the felt from that side and re-applying some new?

Quite often its the lap near the ridge, if the felt is undamaged then no need to replace it, carefully peel back/lift up the ridge piece and stick it back down with a continuous bead of mastic or similar to seal the edge

[Onoff]

Not used it but a few reviews mention sealing felt seams:

 

https://www.screwfix.com/p/geocel-trade-mate-roofers-seal-black-310ml/32561?

 

[AdamD]

On 26/01/2021 at 12:35, markc said:

Quite often its the lap near the ridge, if the felt is undamaged then no need to replace it, carefully peel back/lift up the ridge piece and stick it back down with a continuous bead of mastic or similar to seal the edge

Sorry for the dumb question but ‘the lap near the ridge’?

[AdamD]

Do you think it’s worth putting a storage heater in there to dry to dry the wood out? I’ve got a tarpaulin over the roof for now to avoid further water ingress but the affected area is still quite wet inside.

[Mr Punter]

Good plan to use some heat to dry it out.

[Onoff]

29 minutes ago, AdamD said:

Do you think it’s worth putting a storage heater in there to dry to dry the wood out? I’ve got a tarpaulin over the roof for now to avoid further water ingress but the affected area is still quite wet inside.

 

Dehumidifier?

[Onoff]

31 minutes ago, AdamD said:

Sorry for the dumb question but ‘the lap near the ridge’?

 

See the bit at the very top that goes over the ridge and (in this case) is nailed down. It "laps" over the bit underneath it. Wind driven rain can get up that joint:

 

 

[AdamD]

33 minutes ago, Onoff said:

 

See the bit at the very top that goes over the ridge and (in this case) is nailed down. It "laps" over the bit underneath it. Wind driven rain can get up that joint:

 

 

Got it, thanks for clarifying for a layman ?

 

So in my case would you say remove the nails (mine is nailed down in the same way), peel it back and apply some mastic all the way across the piece of felt underneath, press it back down and bang the nails back in and try that as a starter for 10?

42 minutes ago, Onoff said:

 

Dehumidifier?

I have both so which would be better? Or maybe both at the same time?

[AdamD]

Ok so the overlap is hardly anything, this is surely the issue?

 

 

8916548C-F9D8-4B94-9BC6-87AAED319C55.jpeg

[AdamD]

Ok so the overlap is hardly anything, this is surely the issue?

 

 

image.jpg

[AdamD]

This is the picture I was trying to upload the previous two posts! Hardly any overlap, presumably this is the issue?

 

It’s 1m wide and really I need about 1.5m so I’ve got a 250mm overlap either side. Can’t seem to find felt wider than 1m.

 

Any thoughts how best to do it?

[Onoff]

What way up is it, is the hammer "down slope"? Like this:

 

[ProDave]

I am not a fan of shed roofing felt, in fact I would never put it on a shed.  Lousy stuff with a very short life.

 

I would leave it there as an under felt and over sheet the whole lot with bitumen corrugated roofing sheets, cheap and very water tight.

 

e.g https://www.wickes.co.uk/Onduline-3mm-Black-Corrugated-Bitumen-Sheet-950-x-2000mm/p/240039

 

Link to show what I mean not a recommendation for that particular product from that particular supplier.

[AdamD]

15 hours ago, Onoff said:

What way up is it, is the hammer "down slope"? Like this:

 

Yeah, hammer was sloping down.

[AdamD]

13 hours ago, ProDave said:

I am not a fan of shed roofing felt, in fact I would never put it on a shed.  Lousy stuff with a very short life.

 

I would leave it there as an under felt and over sheet the whole lot with bitumen corrugated roofing sheets, cheap and very water tight.

 

e.g https://www.wickes.co.uk/Onduline-3mm-Black-Corrugated-Bitumen-Sheet-950-x-2000mm/p/240039

 

Link to show what I mean not a recommendation for that particular product from that particular supplier.

That’s a good option. Would you leave all the felt as is now even though it’s saturated the wood? I guess leaving it and giving it extra coverage will allow it to dry out. Don’t think there’s much value in de-felting the roof as the wood will be wet anyway so just needs to be able to dry out now.

[Onoff]

Was the batten the width of where the red arrow is?

 

The bit your finger is on is the factory edge, I think of the 1m wide roll piece used on the apex? There should be adhesive under that bit you're holding up. Where the nails are the adhesive appears to have been applied on top of the green mineral and maybe under the batten?

 

Looks to me like it's done wrong. How far up, does the bit with the nails in poke up under the bit you're lifting up?

 

A shed roof btw should really have a minimum of two separate layers of felt. One underneath then the green mineral impregnated "cap" sheet you have there. How many layers have you got?

 

 

If you must go "one layer" there's a proper way if doing it. This from IKO (one of the big felt producers) for instance. It's good to know to help diagnose where yours is leaking:

 

 

 

 

You don't necessarily need wooden strips if done correctly. They can rot and in fact hold water, forcing it back under a poor lap. Not got any on my 2 layered shed roof. My joins are stuck like sh!t to a blanket. Have to be careful (good) to avoid adhesive dribbles. I just wipe and brush in the mineral "dust" onto any dribble. North facing elevation:

 

 

(I'll finish it one day! ?)

 

Battens can in fact be run up the slope and can look quite good. 

 

My experience of the black, bitumen impregnated roof sheets @ProDave refers to was dire. I reroofed a, shallow pitch, concrete section garage with them (from Wickes). I observed the support spacing requirements by adding in extra angle irons to match the originals. In between the supports the sheets just sunk in like washing up bowl size depressions then split. Poor picture of the roof.

 

 

 

(Ruined a Ford Capri I had stored in there. Salvageable but loads more work than when it went in ? ). 

 

I'd say a one off/bad batch but similar happend to My BiL.

 

In both cases there was no supporting boards underneath I might add but the bumpf on the corrugated sheets said you didn't need it. 

 

Imho I reckon you'd be better with a one piece sheet of EPDM and the proper edge trims.

 

I'll pm you the proper, old school instructions for felting a shed, give me a while.

[Onoff]

Those sheets @ProDave referred to:

 

https://www.wickes.co.uk/how-to-guides/garden-landscaping/fit-corrugated-sheets

 

 

[AdamD]

4 hours ago, Onoff said:

Was the batten the width of where the red arrow is?

 

The bit your finger is on is the factory edge, I think of the 1m wide roll piece used on the apex? There should be adhesive under that bit you're holding up. Where the nails are the adhesive appears to have been applied on top of the green mineral and maybe under the batten?

 

Looks to me like it's done wrong. How far up, does the bit with the nails in poke up under the bit you're lifting up?

 

A shed roof btw should really have a minimum of two separate layers of felt. One underneath then the green mineral impregnated "cap" sheet you have there. How many layers have you got?

 

 

If you must go "one layer" there's a proper way if doing it. This from IKO (one of the big felt producers) for instance. It's good to know to help diagnose where yours is leaking:

 

 

 

 

You don't necessarily need wooden strips if done correctly. They can rot and in fact hold water, forcing it back under a poor lap. Not got any on my 2 layered shed roof. My joins are stuck like sh!t to a blanket. Have to be careful (good) to avoid adhesive dribbles. I just wipe and brush in the mineral "dust" onto any dribble. North facing elevation:

 

 

(I'll finish it one day! ?)

 

Battens can in fact be run up the slope and can look quite good. 

 

My experience of the black, bitumen impregnated roof sheets @ProDave refers to was dire. I reroofed a, shallow pitch, concrete section garage with them (from Wickes). I observed the support spacing requirements by adding in extra angle irons to match the originals. In between the supports the sheets just sunk in like washing up bowl size depressions then split. Poor picture of the roof.

 

 

 

(Ruined a Ford Capri I had stored in there. Salvageable but loads more work than when it went in ? ). 

 

I'd say a one off/bad batch but similar happend to My BiL.

 

In both cases there was no supporting boards underneath I might add but the bumpf on the corrugated sheets said you didn't need it. 

 

Imho I reckon you'd be better with a one piece sheet of EPDM and the proper edge trims.

 

I'll pm you the proper, old school instructions for felting a shed, give me a while.

Thank you so much for your post, detailed and very helpful! 
 

Regards where my finger is,  I do think that is the factory edge yes as this was not applied when the shed went up.

 

It barely poked under at all, maybe 10mm which I suspect is exactly where the water got in and seeped through, it was soaked. It’s not a one layer of felt job but I do think that’s where it got in.

 

I’ve done a patch up today, bought a roll of felt, removed the bit I’m holding up in the picture and started again. Used 3 3m long by 1m wide sheets (one either side with a much bigger overlap and one over the top), used adhesive and many more nails to make it nice and tight up there. Took me ages so hopefully it works!!

[AdamD]

5 hours ago, Onoff said:

Was the batten the width of where the red arrow is?

 

The bit your finger is on is the factory edge, I think of the 1m wide roll piece used on the apex? There should be adhesive under that bit you're holding up. Where the nails are the adhesive appears to have been applied on top of the green mineral and maybe under the batten?

 

Looks to me like it's done wrong. How far up, does the bit with the nails in poke up under the bit you're lifting up?

 

A shed roof btw should really have a minimum of two separate layers of felt. One underneath then the green mineral impregnated "cap" sheet you have there. How many layers have you got?

 

 

If you must go "one layer" there's a proper way if doing it. This from IKO (one of the big felt producers) for instance. It's good to know to help diagnose where yours is leaking:

 

 

 

 

You don't necessarily need wooden strips if done correctly. They can rot and in fact hold water, forcing it back under a poor lap. Not got any on my 2 layered shed roof. My joins are stuck like sh!t to a blanket. Have to be careful (good) to avoid adhesive dribbles. I just wipe and brush in the mineral "dust" onto any dribble. North facing elevation:

 

 

(I'll finish it one day! ?)

 

Battens can in fact be run up the slope and can look quite good. 

 

My experience of the black, bitumen impregnated roof sheets @ProDave refers to was dire. I reroofed a, shallow pitch, concrete section garage with them (from Wickes). I observed the support spacing requirements by adding in extra angle irons to match the originals. In between the supports the sheets just sunk in like washing up bowl size depressions then split. Poor picture of the roof.

 

 

 

(Ruined a Ford Capri I had stored in there. Salvageable but loads more work than when it went in ? ). 

 

I'd say a one off/bad batch but similar happend to My BiL.

 

In both cases there was no supporting boards underneath I might add but the bumpf on the corrugated sheets said you didn't need it. 

 

Imho I reckon you'd be better with a one piece sheet of EPDM and the proper edge trims.

 

I'll pm you the proper, old school instructions for felting a shed, give me a while.

Here’s another angle of the before, complete with our cat inspecting other shed roofs. I think it shows clearly that there was sweet fa of an overlap.

 

Apologies that it is sideways, no idea why it uploads like that.

[Onoff]

1 hour ago, AdamD said:

Here’s another angle of the before, complete with our cat inspecting other shed roofs. I think it shows clearly that there was sweet fa of an overlap.

 

Apologies that it is sideways, no idea why it uploads like that.

 

Sad when good materials are poorly applied! 

[ProDave]

Perhaps the corrugated bitumen roof sheets don't like heat and sags in the Kentish heat of summer? (not a problem up here)

 

I first used it on the wood shed at our previous house and 15 years on no sag and no leaks.  Supported at 600mm intervals.

[Onoff]

4 hours ago, ProDave said:

Perhaps the corrugated bitumen roof sheets don't like heat and sags in the Kentish heat of summer? (not a problem up here)

 

I first used it on the wood shed at our previous house and 15 years on no sag and no leaks.  Supported at 600mm intervals.

 

?  Weird. As per my photo the spans were down to 18" from 3' originally. You might be half right on the sagging/Summer thing. It was a haven for cats and foxes taking a siesta up there. Maybe they were really heavy?