Fixing a cowboy job roof gone wrong... and saving money!

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Hi Guys, new to the forum and DIY in general.

Note, I have no DIY experience at all, except for assembling home furniture.

I had a garden building built in 2018, and now the flat felt roof has already failed and caused a massive leak inside the building. Large puddles form on the roof, and leak down lots of water down inside internal walls and ceiling of building.

I am told that dirt cheap shed felt was used on the approx. 34 meter square roof, and then nailed down (rookie mistake for a builder?) and thus has failed to protect against the UK's rainiest month/year to date, 2021 May.

So I got three quotes so far to fix the damage which range between £3000-7500 for various roofing options.

But I have already spent 4000 pounds the past 2 years just repairing the various things around the building that have gone wrong.

So I have decided to try DIY as much of this as I can myself because Its not worth spending more/large amounts of money to fix this building, and I feel the quoted prices are just a massive fob off!

I have attached photos of the roof, and as far as I know from myself and some other builders the roof construction seems OKAY/SOUND and doesn't need replacing. There is good quality OSB board underneath the cheap felt, but I have not yet inspected the areas where the leak has come through in detail but a builder has walked on top just fine.

My temporary fix solution (Attached Photo 'Temporary Solution'):
  1. Cut out affected plasterboard areas where mould/mildew has formed with carpenter knife

  2. Wait for dry weather and then safely climb roof to brush off any puddles/excess moisture

  3. Guttering needs an additional downpipe and unclogging because it is constantly overflowing even though I upgraded its size last year. The roof area is quite large and needs adequate drainage, I have a 1m cubed gravel soakaway constructed few meters from building for drainage.

  4. Get a 7.2 x 5.4 metre Tarpaulin to cover the top once the roof is dry, and have the Tarpaulin edge facing the PVC guttering side dripping slightly into the gutter for maximum rainwater transfer.

  5. Secure Tarpuline with 10-17 timber (3 metre x 100mm) configured on top according to attached photo at around 6KG each, spread evenly and securing the edge of tarp as per step 4.

  6. Use rope/bungee cords on the eyelets of Tarp on the opposite side to guttering as per attached photo

  7. Dry out inside of building and leaked water



My long term fix solution (again zero experience with any DIY but can ask friends and decorators for assistance):


Perform a DIY installation of a single EPDM Rubber sheet onto the roof using appropriate adhesive.

  1. Wait for warm weather spell and then remove cheap felt and nails from OSB board roof.

  2. Clean and sand down the OSB board and inspect any damp/damage OSB board that needs replacing. Fill nail holes with something like tar??

  3. Carry out Step 2 with either decorate friends or hire someone for any small OSB replacement job (replacing 1 or two units).

  4. Apply adhesive to prepped roof and carefully laydown the EPDM rubber as per instructional videos and using the EPDM DIY KIT. Install a gutter drip trip too.

  5. And then that's as far as my brain has gone! Sorting out the edges/fascia'/edge kerb etc is way beyond my capabilities right now! But hey at least we got a single sheet of rubber on top

Open to any suggestions/comments as I figure this project out!

Many thanks in advance
 

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The puddle has formed because the roof sagged on construction or later and the water has got in between the overlapping felt (or there is a tear).

Sorting that (stiffening the roof joists and maybe a new osb sheet) should address the basic leak, and you can then replace the felt.

Blup
 
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Get a 7.2 x 5.4 metre Tarpaulin to cover the top once the roof is dry, and have the Tarpaulin edge facing the PVC guttering side dripping slightly into the gutter for maximum rainwater transfer

My suggestion would be:

1) buy the EPDM now and put that up there and fix later.

You need about a 300mm extra all around to allow for trimming and overlaps

A 8.0m x 6.1m will cost about £475

You can fix it in place by screwing battens onto the sides.

Or

2) buy a 25m roll of damp proof membrane which will be 4metres wide - use 2 lengths of 8.5 metres and overlap by 1.8m and use gorilla tape for the join - and fix the same way. Put up some weights to stop wind uplift.

I used DPM to keep my 5m x 3m shed dry for 2 years whilst I extended it with a garden office.
 
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B & Q type tarps are too flimsy for anything more than a few days- DPM will do it as suggested above.
Hard to tell from the pics but looks as if there is a decent fall (aim for 5% so 50mm/metre) to prevent ponding.
OSB once soaked loses much of its strength- check sheets carefully.
 
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Open to any suggestions/comments as I figure this project out!
Basically you have a plastered shed. It's so low end that you could trip over it. All the new roofing in the world won't cure the mould either. You will never be rid of the black mould unless you insulate, VCL and ventilate where necessary.
 
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Basically you have a plastered shed. It's so low end that you could trip over it. All the new roofing in the world won't cure the mould either. You will never be rid of the black mould unless you insulate, VCL and ventilate where necessary.
Gosh, I hadn't looked at the pics closely.

It's a warm roof with no insulation.....the moulder is clearly condensation, proper roof covering won't resolve that

Walls appear to be Single skin blockwork?
 
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B & Q type tarps are too flimsy for anything more than a few days- DPM will do it as suggested above.
Hard to tell from the pics but looks as if there is a decent fall (aim for 5% so 50mm/metre) to prevent ponding.
OSB once soaked loses much of its strength- check sheets carefully.

Hi there, what do we mean by fall? 5%, 50mm per metre?

I'll definitely check which OSB boards need replacing!

Okay so no confidence in tarp, switch to DPM, thanks
 
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Basically you have a plastered shed. It's so low end that you could trip over it. All the new roofing in the world won't cure the mould either. You will never be rid of the black mould unless you insulate, VCL and ventilate where necessary.

Hi Thanks for your input, I have no had any issue with black mould on the plaster until this leak with the roof happened, the plasterboard on the ceiling has been in excellent condition!

I dont have any insulation because im not using it as a habitat, just a private place for exercise.

In terms of ventilation I designed a system with two powerful 5 inch inline extraction fans on either end of the building. One to push air in, and another to take out air. Rather than using air bricks because the air volume inside is quite a lot!

I believe this damp has been caused directly from the roof, and we've had so much rainfall recently.
 
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Gosh, I hadn't looked at the pics closely.

It's a warm roof with no insulation.....the moulder is clearly condensation, proper roof covering won't resolve that

Walls appear to be Single skin blockwork?


Hi there, not had any problems with mould/damp/ condensation on the plasterboard until the leak issue happened on the roof.

So I figured I would fix the roof to sort this issue, the are two powerful extractor fans configured inside, that push air in and push air out.

The wall is single skin block work
 
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My suggestion would be:

1) buy the EPDM now and put that up there and fix later.

You need about a 300mm extra all around to allow for trimming and overlaps

A 8.0m x 6.1m will cost about £475

You can fix it in place by screwing battens onto the sides.

Or

2) buy a 25m roll of damp proof membrane which will be 4metres wide - use 2 lengths of 8.5 metres and overlap by 1.8m and use gorilla tape for the join - and fix the same way. Put up some weights to stop wind uplift.

I used DPM to keep my 5m x 3m shed dry for 2 years whilst I extended it with a garden office.

Thank you for the suggestion, so the roof is 7.5 by 4.5 metre.


How am I rolling out the 4 x 25 metre dpm? 4 metre DPM roll going down length way across the 7.5 metre stretch? And then overlap the lengths and leave overhang?
 

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