Observatory repairs and re-conditioning

[Gina]

I wouldn't have thought this was happening bus as Conan Doyle wrote for Sherlock Holmes (something like) "When you have eliminated all probable causes , what it left, however improbable must be the cause."  The EPDM was sitting right down into the bottom of the guttering.  I shall rectify that.

Here are a couple of drawings showing firstly, how I should have done it and secondly a simpler version that ought to work.

But NOT this!

[JamesF]

I'm at a loss as to explaining how the water got there, I have to admit.  I think it might be worth taking at least some of the southern(?) barge board off to see if the water is perhaps coming from somewhere else -- running down the edge, for example, and then stopping at that corner, perhaps because there's nowhere else for it to go, with the ply sitting in it.

I'd also be inclined to keep the guttering in your case Gina, because otherwise dripping water might be driven back through the gaps around the fold-down section of the wall by wind?

I wouldn't choose to have the EPDM sitting in the gutter myself because I'd prefer to see everything clear of the water, but I'm not sure it's going to be damaging in this case.

James

[JamesF]

Depending on the amount of damage to the edge of the ply, I might be tempted to extend it over the gutter position and then fold the EPDM back up and underneath, fixing it back to the top of the wall, perhaps with a small batten or a strip of aluminium.

James

[Gina]

The edge of the ply is no longer there having removed most of the rotten part.  I'm going to take the guttering off and see how much EPDM there is sticking out from the roof.  Also, removing the end where the down pipe is will release more EPDM and may show something.

[Gina]

I've taken the guttering off and was able to get at the inside of the EPDM on the inside of the barge board and the timber strip just inside that holds the EPDM up at the edge to stop rainwater running off the roof and inside the barge boards.  Both completely dry.  The wettest ply is definitely in the SE corner, so that's where the wet is coming from.  Maybe splashing up at the end of the guttering which is almost touching the main roof timber.  There is no sign if any rot in any solid timber - only in the ply.  Along most of the length of the edge there is about 4" EPDM extending from the edge.  For a few inches at the south end this reduces to around 3".

Here's a diagram of the sides of the roof.

[Gina]

Removed the rest of the guttering, end fittings and brackets.  There was wet behind the down spout so I reckon the small guttering and end spout plus down pipe have been too small for the amount of rainwater coming off that half of the roof.  The size is about 8ft x 4ft.  I shall replace the mini guttering with full size and stuff a sheet of acrylic 4ft x 2ft between EPDM and remaining ply and roof timbers.  I'll have to go out to the big shed and see if I have a length of battening to put between EPDM and roof framework.  Meanwhile, I need a break and a cuppa!  Won't be doing any more to the observatory today as the wind has got up and it's turned cold.

[Alan White]

Sounds like solid progress Gina.

I am of the opinion capillary action has been taking place and over time, soaked the ply in a ceaseless manner.
You would be amazed how far water can be drawn by capillary action on roofing.

[Gina]

Yes, I too think it's capillary action and I reckon it's water splashing up from the down spout.

[Carbon Brush]

Not sure if this might be contribution to full gutters..Leaves.

A few wet leaves can increase water level in the gutter, and block down pipes. Later you go and look and the leaves have rotted, or blown away.

Just a thought.

David.

[Gina]

Possibly but there aren't any trees nearby.

[Astrokev]

Good progress to diagnose the cause Gina. Certainly a tricky one. 

I wouldn't have thought EPDM would wick water by capillary action as it's totally non-absorbent. However, if the EPDM is dirty due to general accumulation of surface dust/dirt over time, I guess it's possible this could create an absorbent layer that could act as a capillary. 

Your proposed solutions sound good.

For my own build, based on the above unsubstantiated theory (?) I think check the edges of my EPDM over the gutters  If there's a chance this may become submerged beneath the water running in the gutter I think I'll trim it back a bit.

The edges of my EPDM are stuck down with solvent based adhesive, which are probably more resistant to water exposure. This may be something for you to consider?

 

[Gina]

Yes, I have considered a solvent based adhesive but that needs warmer weather, I gather.  I will just have to be clamped of clout nailed.

[Carbon Brush]

I used a water based adhesive (PVA from memory) on my observatory. It had to be weighted or clamped for days as each section dried. The water took ages of course to soak into the ply.
But it has held together for 11 years. In the cold, it could take weeks for this approach to work. Then if you get a good frost before the adhesive has cured, you could have problems.

A shed I roofed two years ago used a solvent adhesive. The biggest difficulty was getting the job done quickly. It was summer and the solvent exaporated quickly.
This roof has held together without issue and was strong very quickly.
The solvent is one of those that strips the lining from your nostrils and makes virds fall out of trees. But it works well. Smell like the old fashioned impact adhesives before we made 'safe' glue'
If I used too much, it actually softened and expanded the rubber.
In this weather you won't have to rush as I did. And you won't have to worry about the frost - provided your wood is dry.

This is the stuff I used. I bought a 5 litre can.

https://www.bonnymans.co.uk/products/product.php?categoryID=1391&productID=6139&noindex=

To apply, I decanted it into an empty baked beans can, then spread it by brush. The easiest way of working on the roof.

Don't even think about cleaning your brushes afterwards! They stick into the tin.

Don't sniff the vapours. You will probbly fall off the roof and not know it!

David.

 

 

 

[JamesF]

The solvent-based adhesive used by Rubber4Roofs (who I think quite a few of us have used) is much the same.  It goes off if you so much as look at it in a funny way.  I remember Kev did his during the late summer/early autumn on a relatively warm day and had to work very fast.  I did the roof of my warm room when it was much cooler and it was still a bit of race.

James

[Astrokev]

Yes, I used the rubber4roofs stuff. As James said, first application was in summer. Dried really quick so I had to work fast, but apart from that it was fine. 

Dont try and apply with a roller, it just gets goo'd up. As David says, use a brush then throw it. 

I recently used it in colder weather and the glue was much easier to use - but the EPDM was less flexible, but I managed ok. I think the recommendations to use it in warm weather are more to do with ensuring the rubber is flexible rather than the glue.

 

[Adam J]

My guess is that its rain water falling directly into the gutter and splashing back up against the end of the ply. I would think that the membrane is then preventing it from evaporating and over the course of years that has built up until the membrane detached accelerating the end.

[Gina]

Picked up fittings for the 4" guttering I plane to use on the roof from town today.

[Gina]

Haven't decided yet how I'm going to extend the roof edge to take the EPDM over the guttering.   I can't get a piece of wood long enough in my little car, I've measured it.  I might have to use more than one piece, joined in the middle.  Or if I'm joining things anyway, I could 3D print 5 pieces that interlock with whatever shape I desire.

[Jkulin]

35 minutes ago, Gina said:

Haven't decided yet how I'm going to extend the roof edge to take the EPDM over the guttering.   I can't get a piece of wood long enough in my little car, I've measured it.  I might have to use more than one piece, joined in the middle.  Or if I'm joining things anyway, I could 3D print 5 pieces that interlock with whatever shape I desire.

Hi Gina,

Can you not open a rear window and tie it in place, I've done that loads of times with success, I have even got a 9ft length of wood into my convertible two seater.

Or conversely which I have seen done loads of times is to wrap the wood with cloth and tie it to the outside of the door pillars, perfectly safe and won't harm anyone.

[Gina]

I'll check again but I don't think either of those would work within the law.  Tying to door handles is no-go because it's only 2 door (or 3 if you include the boot).

[Dr_Ju_ju]

Using long webbing straps, put the timber onto the car roof (with suitable weight spreading and soft padding), then use the webbing straps to tie it down firmly, both front & rear, with doors open. then closing the doors will tighten down even more.... 

I have used this technique one or twice, when having to transport some 7M beams ?

[Gina]

Just back in from the observatory.  I don't think I shall be working out there much today unless the weather improves.  Turned cold and damp.

Checking the bigger guttering and looks like I might have a problem.  I thought the guttering was 4" (100mm) but it's actually 112mm and the brackets are too high for the end beam of the roof frame and would stop the fold down window opening.  OK I know, I should have checked.  I may be able to get away with the big guttering if I can make my own brackets - I think the bottom of the actual guttering would clear the top edge of the window frame.  The guttering will have to go as high as I can get it (whilst allowing a slight slope) which impacts on how the EPDM is supported.  I shall be working my brain in combination with CAD software!

[Gina]

Don't think my brain was working properly yesterday - too keen to get stuff to do the job.  Just been Googling and found how to calculate what size guttering I'd need and it turns out that the mini guttering should be well able to cope with half my ROR runoff by a factor approaching 10x.  I think this is optimistic and may not be taking account of the extreme downpours we are getting these days!  I may get some new mini guttering as the current piece has pieces broken out of it. 

[Peter Drew]

Don't overdo things physically as a result of your resurgent enthusiasm Gina!. Guilty of this myself on many occasions.   ?

[Gina]

Good advice!  Thank you.  I think I did rather overdo it yesterday.  I'm going to take it easy today...