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Not quite a workshop.Advice please.

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Not quite a workshop.Advice please.

Postby firedfromthecircus » 10 Oct 2018, 10:27

Hi Folks.
Apologies in advance for this not being a workshop build, or indeed woodwork related, but since I joined this forum a few years back I have been very impressed with the knowledge of the forum members and I can't think of a better place to get advice. :eusa-clap:
So on to the problem.
We have a bomb shelter in our garden which was converted into an office for my wife. The problem is that there is a little water ingress and we would like to improve the roof to try and fix it. The shelter is built in brick with walls about a foot thick and a concrete roof. There is no overhang so any rain just runs from the roof and down the walls. I was wondering if some form of roof construction on the top of it with felt or EPDM covering, and with an overhang would improve the situation. Trouble is the building is 3.3M long so not a simple 'one sheet' size, and despite being a member of a woodworking forum my skills in that department are seriously lacking!
The concrete roof slabs do have a couple of cracks which don't seem to go all the way through (they are totally solid) and the pointing on the walls has had ferns growing in it. Despite my wife liking the cutsie aesthetic I have finally persuaded her that we have to remove the ferns and fix the pointing which I am guessing will help a lot. But will that be enough?
So what would you do, bearing in mind a preference for both a low cost and low skills fix?

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Re: Not quite a workshop.Advice please.

Postby Mike G » 10 Oct 2018, 12:14

Re-pointing (with lime) will help, but it wouldn't solve the fundamental problem. I would certainly put some sort of sheet roofing on that building if it were mine, (maybe even slates), with some decent eaves overhangs (minimum of 100mm). This would also enable you to put gutters on and thus get the roof-water away from the footings and the lower part of the wall. This is all very easily achieved, and a cheap job.
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Re: Not quite a workshop.Advice please.

Postby Robert » 10 Oct 2018, 13:27

firedfromthecircus wrote: Trouble is the building is 3.3M long so not a simple 'one sheet' size,


EPDM comes it almost any size you want and 3.3m+ would be no problem.

My last adventure with EPDM is here -

viewtopic.php?f=26&t=3472

Guess you'd still need a wooden covering to put it on so still a lot of work.
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Re: Not quite a workshop.Advice please.

Postby firedfromthecircus » 10 Oct 2018, 15:06

Robert wrote:
firedfromthecircus wrote: Trouble is the building is 3.3M long so not a simple 'one sheet' size,


EPDM comes it almost any size you want and 3.3m+ would be no problem.

My last adventure with EPDM is here -

viewtopic.php?f=26&t=3472

Guess you'd still need a wooden covering to put it on so still a lot of work.


I read your EPDM adventures Robert. Good job. I saw you can get EPDM in big sizes which is what lead me to think of that rather than roofing felt, but it's the ply or OSB sheet sizes I was referring to. It would be a lot easier if it was one sheet long!

Mike G wrote:Re-pointing (with lime) will help, but it wouldn't solve the fundamental problem. I would certainly put some sort of sheet roofing on that building if it were mine, (maybe even slates), with some decent eaves overhangs (minimum of 100mm). This would also enable you to put gutters on and thus get the roof-water away from the footings and the lower part of the wall. This is all very easily achieved, and a cheap job.


Thanks Mike. I am certain this would be an easy job for you but sadly we are not all endowed with your knowledge and skills. I am struggling with what the extra roof structure would entail, and how to fix it all to the shelter, particularly where the sheets of OSB would need to join and any battens across the length. Joining the lengthwise eaves bits too. I had thought that it could be fixed with rawl bolts into the brick at the gable ends but I'm not sure about doing the same along the sides. Also no idea if trying to fix directly to the roof would be a good idea. I'm a bit lost tbh, and thinking about how I could do it is hurting my head! :lol:
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Re: Not quite a workshop.Advice please.

Postby Mike G » 10 Oct 2018, 16:00

OK, well let's work out one way.

Take some ex-2"x2" treated timber, measured as, say, 150 longer than the current ridge-to-eaves distance, and screw them down the slope of the roof 2 feet apart. The top of each new "rafter" aligns with the current ridge, and so the bottom end overhangs 150mm.

Next, screw some of the same size timber on top of the "rafters" (they feel more like counterbattens than rafters), starting with one on top of the eaves, and then every 2 feet to the top, and finishing with one sitting one the end of the rafters at the ridge. Next, fiddle in something at the eaves to stop insects and vermin getting in, but which allows air flow. This will involve extra bits of wood, and some mesh.

Finally, nail your crinkly tin, Onduline, or similar corrugated product on the top to the manufacturer's specification, and fit their ridge over the join at the top.

-

Finally, and most importantly, are you sure the building is leaking? Unless it is insulated, which won't be easy, then there is every chance that a building like this would have an enormous condensation problem if someone is working inside it. On cold days it could easily be running down the walls. It may be that you have a very different problem from the one you thought you had.
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Re: Not quite a workshop.Advice please.

Postby firedfromthecircus » 10 Oct 2018, 16:35

Cheers again Mike.
That is a completely different way than anything I had thought of, which exemplifies why I am asking! :lol:
Couple of questions. Firstly, can I screw the first set of timbers directly to the concrete roof slabs? What kind of fixings would you recommend?
Secondly, with an anti-insect mesh fitted how well would a roof like this deal with wind? The top of the garden does have some shelter but it can be pretty windy at times (East coast of Scotland). One of my concerns is losing whatever I attach come the first winter storm!

Regarding leak or condensation. The initial conversion work was done by someone else but it was fairly well insulated, and there is ventilation with a window vent. It is quite possible that condensation is an issue, but the thinking is we have to be certain it's really weather tight before we know if we need to tackle that problem later. Does that sound about right?
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Re: Not quite a workshop.Advice please.

Postby Mike G » 10 Oct 2018, 16:41

Simply screw and plug the timber down with plastic plugs and appropriate screws, or, if you really are worried about an exposed location, bolt them down with rawl-bolts. Those would need bigger holes, though, and drilling them might start to cause a disturbance inside, so I'd be inclined to just add some extra screws and plugs.

If it is insulated and ventilated it is less likely to be suffering condensation, so yes, sort the roof first, then re-point, then see if any dampness issues remain.
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Re: Not quite a workshop.Advice please.

Postby jules70 » 10 Oct 2018, 21:37

Personally would love to see a natural slate roof covering to any brick building like that. Would look so much better than a few sheets of tin or a rubber roof ! Just my opinion of course.
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Re: Not quite a workshop.Advice please.

Postby TrimTheKing » 10 Oct 2018, 23:56

Lovely looking little building and I agree with Jules that it would look great slated.

I slated my roof just by asking questions on here and looking at tons of YouTube videos and it really isn’t difficult if you google the principles and have an ounce or two of common sense and DIY ability.

Depends how much you want to spend but slates wouldn’t break the bank and would look awesome.
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Re: Not quite a workshop.Advice please.

Postby Mike G » 11 Oct 2018, 07:48

There's quite a difference in cost between slate and sheet materials. When the OP suggests felt, and stresses a low-cost low-skill solution, then slate at around £30/ sq m is clearly not on the agenda. It would be the nicest roof, obviously.
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Re: Not quite a workshop.Advice please.

Postby RogerS » 11 Oct 2018, 08:22

One question is this ..you mention water ingress but I missed exactly where it's 'ingressing'. Drips from the ceiling? Damp patches on the walls ? Depending on that surely dictates where to apply the 'fix'.

I love the setting....looks like it's inset into the side of a rocky hill ? What size are those blocks/bricks/stones in the wall ?
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Re: Not quite a workshop.Advice please.

Postby firedfromthecircus » 11 Oct 2018, 10:10

Thanks for the comments folks.
I agree that a slate roof would look much better than anything else, and it would match the house.
I initially thought some boards and felt would be a really simple and cheap job. Then found out about EPDM. Then discovered it would be a little more complex than I thought and the costs are rising too! Looking at the price Mike has given for slate per square meter it might not work out that much higher in cost, and perhaps it would be worth it. So some more questions.
Would laying slates start from a similar point in terms of laying a frame for them to sit on?
How much harder would it be?
Can anyone point me at some good resources?

Regarding the pointing. You mention Lime pointing Mike. Any reason to specify Lime than any other kind of pointing? (Bear in mind I don't know what kinds of pointing there are!)

One idea from left-field here. Being on the East Coast of Scotland pantiles are a common feature and our village has a mix of slate and pantiled roofs. What would be the difficulty and relative cost of fitting pantiles? Could they be laid direct on to the concrete roof and mortared in? :eusa-think:

To answer your questions Roger. There is some dampness above the window on the other side of the building and I think a bit near the door. Because of how the building and the interior have been constructed it is very difficult to tell if water is actually getting in, and if it is from where. There are no leaks as such but possible creep, which could be from a number of sources. My thinking is to tackle it methodically until it is sorted and the first issue (aside from the ferns in the pointing) is to ensure the roof is completely water tight and stop the rain running directly down the walls.
The bricks are normal brick sized and it sits at the top of our garden in front of a rock wall that is about 12-18 feet high. I guess they chose the siting just for the extra protection it offered. During the war they created a dummy airstrip out the back of the village so the Germans would bomb it rather than the nearby airfield and since they were actively directing air raids to this location they built an air raid shelter in all the gardens. :text-bravo:
It is a cute wee building and a nice feature in the garden and my wife loves having it as her office. Of course it would have been a lot cheaper, easier and more practical to just build a dedicated office, but that wasn't suitable for some reason! :lol:
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Re: Not quite a workshop.Advice please.

Postby Mike G » 11 Oct 2018, 10:45

That roof looks too slack (ie too low a pitch) for pantiles. Slates can be used down to 22.5 degrees, and so look the most suitable. Pantiles would still need fixing to battens, but as I say, I don't think they'd be suitable for this roof.

Slating that roof would be relatively easy. The same principle as before of "rafters" (they're really counterbattens) running down the roof, then you'd fix 2"x1" battens across the roof at 200 centres (if you were using 250 x 500 slates). The slates come pre-holed, so the only work you'd need to do to the slates would be to cut one in half lengthways at the end of each row. Other than that, it's just a question of nailing it on. Your difficulty comes at the verges, and at the ridge. The verges you could just cover with a barge board (say 4x1), so pretty straightforward, but the ridge needs ridge tiles bedded in mortar. If you haven't done this before, it's not easy, so you might have to allow some money for half a day from a local builder to do it for you. You have to leave the top couple of course of slates off the roof on one side for access, and he'll fix those as he goes.
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Re: Not quite a workshop.Advice please.

Postby RogerS » 11 Oct 2018, 10:56

I can answer the lime-mortar question. Basically lime mortar, as opposed to any of the cement based mortars, allows the joints and wall components (bricks, stone etc) to breathe. Any water getting in can gradually evaporate away. It is very easy to apply. if you wanted a trip to Edinburgh then Masons Mortar run courses but TBH it's a doddle.

If you type in 'galletting' into the search bar, it should take you to my posts on doing some.

If I was in your position, I'd break out the old mortar above where the damp is above the window and repoint using lime mortar.I'd check the joint between the roof and the top row of bricks there as well because I can imagine a crack between the two letting water in.

You could open up any small cracks in your concrete roof with a small angle grinder and then put in lime mortar using a finer sand than you would for pointing. Then quite honestly I'd wait and see how things went rather than go to the expense and hassle of a new roof.

Do you have any photos of the damp areas ?

Whereabouts on the East Coast of Scotland are you located ?
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Re: Not quite a workshop.Advice please.

Postby jules70 » 11 Oct 2018, 21:33

Mike G wrote:That roof looks too slack (ie too low a pitch) for pantiles. Slates can be used down to 22.5 degrees, and so look the most suitable. Pantiles would still need fixing to battens, but as I say, I don't think they'd be suitable for this roof.

Slating that roof would be relatively easy. The same principle as before of "rafters" (they're really counterbattens) running down the roof, then you'd fix 2"x1" battens across the roof at 200 centres (if you were using 250 x 500 slates). The slates come pre-holed, so the only work you'd need to do to the slates would be to cut one in half lengthways at the end of each row. Other than that, it's just a question of nailing it on. Your difficulty comes at the verges, and at the ridge. The verges you could just cover with a barge board (say 4x1), so pretty straightforward, but the ridge needs ridge tiles bedded in mortar. If you haven't done this before, it's not easy, so you might have to allow some money for half a day from a local builder to do it for you. You have to leave the top couple of course of slates off the roof on one side for access, and he'll fix those as he goes.


Alternatively go for a dry fix ridge, and mechanically fix it down. (A better way to go than your traditional mortar route in my humble opinion). Also should be within the scope of a competent diy'er to do.

Can i put on record ! Really dislike a dry verge with horrible big pieces of plastic overcloaking, especially all universal ones that dont really fit very well. So my preference dry ridge, traditional verges !!
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