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New workshop building advice.

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Brian Abbott18/05/2018 14:12:05
319 forum posts
51 photos

Thanks for the advice guys.

Builder seems adamant that this is what he has always done and never had any problems, given the nice work he has done up to now i cannot argue.

Howard Lewis18/05/2018 15:00:34
1161 forum posts

+1 for rubber roof, rather than felt. Felt lasts about ten years, EPDM rubber roof is usually guaranteed for twenty, but has an expected lifespan of fifty.

Garage roof was Pirellasti, laid by professional installers, troublefree for the last twenty plus years.

Workshop roof, (much smaller 11' x 8' ) laid by a friend and myself, in less that a day. What took the time was removing the bitumen adhesive used for the original felt!, with a heatgun and scrapers.

Rubber For Roofs were the supplier. Their website has a calculator which works out size of the rubber sheet required to cover a roof of a given size, (allowing for overlaps on edges). It also helps work out what trims are required.

Ordered during afternoon, arrived 0800 next morning. Clear instructions, adhesive, brush and rollers, and more than adequate rubber, trims, fittings and roundshank nails were in the consignment.

Makes for a neat, weatherproof job. Am still using the slight excess rubber cut off after the trims had been nailed into place, for various small jobs.


Edited By Howard Lewis on 18/05/2018 15:01:10

Rob Rimmer18/05/2018 16:32:45
36 forum posts
1 photos

+ another 1 for rubber roofing - replaced my parents' garage flat roof about ten years ago, no trouble with it, and since then have recommended it, and helped install it, on friend's roofs as well. As always, preparation is the key to success, and try to get it completed before it rains (which is what happened to me )

Mick Charity18/05/2018 17:55:32
199 forum posts
4 photos

A chap I used to work with made his fortune in flat roofing.

Whilst having the greatest respect for his buisiness acumen, he was also one of the most funniest people you could hope to meet this side of a comedy stage.

Apparently there are only 3x truths in the whole wide world. "You were born, you will die . . . & flat roofs leak"

When offered the problem of all of these new fangled rubber EDPM roofing systems & how it will affect the flat roofing business, his reply was . . . "Come the next ice age, can you see the only remnant of the last civilisation being a flat roof locked in & slowly floating along with the glacier"?

Does he have a point?

The only 3x truths in life you can guarantee are, 1: You were born. 2: You will die. & 3: Flat roofs leak.

Anything else is marketing bollox.

Raymond Anderson18/05/2018 18:15:19
694 forum posts
132 photos

Brian, As a Bricklayer / Mason, Your builder is correct, no need to take the Dpc up the face of the internal wall. Good practice is also to "dowel " the new floor slab into the existing floor slab. It's only a case of rebar doweled and resined into the existing slab and projecting into your new slab by 200mm and at 300mmm centers. Saves any settlement later on.


Edited By Raymond Anderson on 18/05/2018 18:23:08

Bazyle19/05/2018 00:44:27
3910 forum posts
166 photos

Moved into a place with a flat rubber roof extension. Put up with summer heat induced plastic pong for 15 years but after doing my garage in 3 layer felt I had the confidence to do the house when it started leaking . Both been good for 18 years. The plastic one was susceptible to cats and squirrels slicing it with their claws which then split when winter cold shrinkage put it under tension. For a design with enough slope I would use insulated steel sandwich factory style.

Brian Abbott19/05/2018 21:26:21
319 forum posts
51 photos

Thanks again all, not even start worrying about the roof, be a nervous wreck..

Raymond, thankyou, just the anwser i wanted.

The ground at the back of my new workshop is slightly higher so i have asked my new best friend ( i am sure the feeling is not mutual ) to lay another course just so i can keep about 150mm from finished ground the top of the brick,

When i attached the wall plate should i bed this on morter or just screw it down with a dpc in between ?

Thanks for any help.

Raymond Anderson20/05/2018 06:18:18
694 forum posts
132 photos

Technically the Wallplate should be bedded on to Lime [ although Mortar is most often used now.] Yes the DPC should be under the wallplate. If your bricklayer has all the bricks / blocks flat and even [ in relation to each other ] then you can omit the mortar bed just make sure the wallhead is clean and FLAT. Best to use drive in fixings for fixing the wallplate to the wallhead. I always use the Bitumen type DPC as it is better "self healing " around the fixing holes although even the polyethelyne type never gives any problems. just my preference.

DPC should always be a minimum of 150mm above finished ground level. the correct procedure is DPM from the floor should come up and also lap onto the wall head together with your DPC. the DPM / DPC should all be at finished floor level

Adam Mara20/05/2018 18:03:59
25 forum posts
4 photos

re roofing. I built a brick workshop in the seventies, big six asbestos roofing at the time. In 2010 a big unit was built at work and roofed with 100mm Trisomet insulated panels. Left on site were 3 and 4 metre lengths offcuts of the sheeting. I used them to replace the asbestos sheets, making sure the overlaps were well mastic'd! Not had a leak at all, which is more than can be said for the unit roof!

Speedy Builder523/05/2018 21:33:07
1470 forum posts
99 photos

Not to hijack this thread, but in the next few weeks, I will be building a wooden garage (waiting for the timber to be delivered). The walls will be made from T&G Douglas Fir weatherboard and treated with a natural non waterproof "lifetime wood treatment". This allows the wood to weather naturally (shrink and swell) but prevent rot and fungus. Question, how 'tight' should I fix the boards against each other. Should I "jack" each plank against each other and not allow for any expansion (widthwise) or should I just place the planks naturally. Planks will be nailed to the upright structures every 900mm.

Ps The wood yard say that the timber is autoclaved before the T&G profiling is machined.


Bazyle23/05/2018 23:24:10
3910 forum posts
166 photos

I have a dead cheap t&g shed and the gap between the 3in boards changes by at least 1/8 in over the seasons. T&G is the worst possible joint for an exposed situation. The tight fit means the water wicks straight through. There is a reason why featheredge and shiplap were invented.

If you get the gap wrong when it gets wet and is too tight it will buckle, if too loose when it gets dry it might spring the tongue out of the groove. in this weather I'd get it bone dry and fit it spaced just engaged using a metal spacer all along to get it even.

bricky24/05/2018 00:12:12
281 forum posts
30 photos

Speedy,Don't use T&G boards for the reasons Bazyle gave ,shiplap always needs regular painting .Rough sawn Feather edge boarding is the best and painted with masonry paint it should not need painting for about 10 years.


Speedy Builder524/05/2018 06:47:32
1470 forum posts
99 photos

I am using the same T&G weatherboard as my workshop which I built 14 years ago and is serving admirably, no leaks no warping, warm and dry - no condensation, its just that I don't remember how 'tight' I placed the boards together. Ship lap is fine if you like drafts between the boards when they warp. My dad said that when the wind blew, the windmill where my grandad worked was like working in a cloud of dust - shiplap !!

Bazyle24/05/2018 09:36:44
3910 forum posts
166 photos

Draughts? plan for a vapour barrier plastic sheet inside the insulation taped at every join. You don't want condensation forming on the inside of your wood walls.

Brian Abbott12/06/2018 13:19:25
319 forum posts
51 photos

Well me new sheds coming along, base is down, frame is up.

Plan is to wrap it in a breathable membrane, then clad in ship lap leaving a 20mm air gap.

Does anyone know if i can use standard roofing membrane ?



Brian Abbott13/06/2018 12:29:32
319 forum posts
51 photos


Anyone know about the breather membrane ?


Bazyle13/06/2018 12:50:44
3910 forum posts
166 photos

You put the breathable membrane on the outside, under the shiplap just to discourage drips and flies and reduce air movement in high winds (normally used under roof tiles and not essential on a wall with good cladding) Then you have the insulation and a non-breather vapour barrier before the inner plasterboard or ply inner sheet. It is the vapour barrier that is most important as it stops the moisture inside going into the insulation and condensing inside it causing internal mould and rot. It does mean you need to ventilate inside the room or use a dehumidifier to remove the up to 6 pints of water a human produces a day.

Bazyle13/06/2018 13:13:14
3910 forum posts
166 photos

Roofing membrane/breathable membrane is not waterproof or a vapour barrier (even though some clever builder type thought it was a good idea to power screw it over our leaking shed at the cricket club). You need either plastic sheet or foil covered insulation board with the joints taped over.
A small gap around solid foam insulation boards being fitted in between frames is not ok Warm air heads for the gap and negates a lot of your effort on insulation. This is why two overlapping thin sheets is better than one thick and in the highest specification jobs the innermost layer is continuous over the framing though that makes the inner sheet less firm for hanging shelves etc.

Raymond Anderson13/06/2018 14:49:38
694 forum posts
132 photos

Brian, The "breather " membrane you mention is mostly used in Kit construction ie the inner walls are 140mm studs and either 9mm ply or 9 mm osb fixed to the studs [ cavity side ] then the cavity and then the outer leaf of Brick / Block. Never known it used on a wooden shed.... but then I've never built any wooden shedssmile

Brian Abbott13/06/2018 15:11:44
319 forum posts
51 photos

Thanks guys for your reply's

My plan is to build as per the 'reversed timber frame', so i have the plywood internally to give me the strength, then the 95 x 45 frame insulated with something or other, then the membrane, battens for air space then the cladding.

Ok, will add the membrane for what its costs, won't hurt.

Thanks all.


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