Thermal insulation for a wooden shed: advice, please.

[CambridgeWorks]

Not wishing to pusue OT further, but I just ordered some Barretine for 20% discount to £18.98 by following a link to toolstation from the Barretine website. Free delivery as well. A job to do sometime before winter as the shed has had just one treatment since built 8 or 9 years ago. The original treatment was with a Sovereign brand product that has lasted very well.

I have 2 workshops, indoors small bedroom and outside shed 12x8 feet nom. It is insulated with 50mm thick blue insulation. Sorry, don't know the name, but it is commercial grade. Cut with a saw and fixed between the battens. Roof and floor insulated as well. Floor is then laid with waterproof t&g chipboard glued at all the joints to provide a rigid platform.
Colder weather has a de-humidifier running about 2-3 hours daily, set to max and controlled by a timer. Car boot and freecycle being where my 2 came from. One is on the landing near my worksop door.
The 5ft long bench has a piece of high quality kitchen worktop mounted on a home made 4x2 inch frame. Solid enough for an RA17.
Rob

[David Simpson]

45 x 45mm sounds a stronger deal than some of the cheapo thinner shed studding sold by B & Q & the like. 45 x 45 is the 'dressed' size of good old 2 x2" W/W O/S.
Just as important as structural & internal cladding - is the site it sits on. Slabs, gravel, rough earth, what ? Hopefully its raised up at least a brick high(approx. 3"), and as well as the outer wall plate being supported - the flooring joists(45 x 45 ?) will need supporting at their centres. Also slip off-cuts of builder's DPC between the timber & bricks or whatever it sits on. If its on a big slab of concrete or paving slabs, and you've no guttering - then heavy rainfall falling from the roof will 'splash-back' upwards & soak the bottom timbering if its too low. Maybe 6" concrete blocks would give you more height. Then consider the wind - if the site is exposed - buy some builder's galvanized h/duty strapping & concrete the 1m lengths into the ground at each corner. Then the matrix of holes in the strapping make it easy to screw into the wooden shed.

Regards, David

[Tractionist]

Ho! Advice coming in fast and rapido! Yep I could talk about psychometrics, vapour pressure, temperature and dew points etc. .... but the key is: ventilation and an effective vapour barrier.

With regard to interior linings: most 'off the shelf sheds' comprise a framing made up of vertical uprights [AKA 'studs'] and some horizontal members of the same cross-sectional dimensions [AKA 'noggins']. However - virtually all lack diagonal WIND BRACING ... necessary to prevent 'racking' in framed structures [often causing the demise of sheds and caravans etc.]. A semi-structural lining [as per the sterling board that I previously suggested .... or more expensive plywood] will also serve the purpose of a wind brace 'membrane'.

On the subject of roofing material [finish] - the best [in my opinion] is granular finished pressed galvanised steel 'look-a-like' interlocking concrete tiles. These are lightweight and come in long strips emulating/simulating a row of real concrete tiles. These are available in a variety of granular/mineral colours and were originally invented in New Zealand. They are not cheap - but a lot cheaper if obtained from a reputable supplier as opposed to a shed retailer. (Naturally matching gable and verge components are available too ...).

The ultimate roof finishes are Welsh Blue Slate and copper or lead - I've been on lead roofed Cathedrals with finishings approaching 1000 years old. However, the specialist labour associated with slate, copper, and lead ..... and the cost, weight [and labour] associated with lead, make these materials wholly unsuitable for use on a lightweight non-habitable timber-framed structure. (Not to mention the risk of larceny ...). However - anything is better than a single sheet of lightweight jute reinforced bituminous mineralised felt!

Hope this helps ....

[ms660]

Here's a shot of part of one I built, its about 30 ft long, cladded with extra thick shiplap which I had specially milled to my specs for a decent overlap, just finished doing the facia brackets, facia and guttering with my trusty Makita cordless when that photo was taken, brackets were needed 'cos the roof has an overhang wider than is normal for a shed, that was to allow 1.8 metre roofing sheets to be used without having to cut them to length, brackets made from 2x2 (uprights and horizontals) and 2x1 (diagonals)

It's unheated by the usual means apart from on the odd occasion, quite good solar gain, trickle vents on windows left permanently open, also a bit of ventilation via gaps around the service pipes etc. Internal finish is T/Edge 12.5mm plasterboard, joints scrim and fill, boards not skimmed. 12mm racking boards on the outside faces of the studs, insulation is a mixture of foil backed foam (Xtratherm) and Rockwool, the plasterboard is the vapour barrier (foil backed) There's a 25mm vented air space between the exterior cladding and the racking boards.

The joint gap between the walls and the ceiling will be covered by a thin timber strip......At some point....

The roof covering is 3" profile fibre cement sheets (not asbestos fibre) with clay ridge tiles, the roof timberwork is purlins only on braced trusses (apex roof)

The whole thing is off the ground on concrete blocks by about 18". Insulation fitted between the floor joist, floor is 18mm shuttering ply.

Not far from the coast, rain can be horizontal in the winter, no condensation, damp or mould.

Lawrence.

[Radio Wrangler]

That looks better built than some houses I've seen, Lawrence.

I've spent a number of years rebuilding the granary of a watermill. All new pressure treated 9" x 3" joists. Inch thick floorboards for the hay loft which I had to tongue and groove myself. New truss A-frames.. full new roof timbers and boards. Now in membrane and I'm slowly re-slating it. Made a new staircase with treads and rails out of 9 x 4. This is an agricultural building which is staying that way, not a conversion.

David

[dave walsh]

The info on vapour barriers, ie whether they should be internal or external, is sometimes confusing. I think that the Regs are often based on the idea of a domestic living space with lots of moist air generation. Some of the designs here are so well thought out and over engineered [only a possibility privately now] that either way, it would be hard to go wrong!

I live in two, basically not well insulated dwellings but with regular monitoring and a common sense ventilation approach you can do ok. After all most people don't even appreciate or think about it so there might be nothing at all, inside or out! My shed in Rammy is obviously on its last legs but it's lasted thirty years... just because I put it on a sub-frame and not directly on the ground!

Dave W

[Skywave]

My response to post #22 by David Simpson.

The foundation is a concrete slab. (A slab was already in existence when we acquired this house: I simply extended it; doubled the length). On that are a number of tanalized bearers about 4 inches square which run across the entire width of the shed. In total, there are about 6 bearers; the length of the shed is 15 feet. The shed floor rests on those and between that floor and the bearers, wood shims have been added to provide a horizontal floor, since the concrete foundations have a slight slope throughout the length of the shed. This slope (which was not specifically designed to be sloping, the land is just that way) will help rainwater that gathers under the shed to run to a nearly drain.
The floor itself is one inch wide T & G softwood. Internally, I have covered that with hardboard: that, in turn will be covered with lino at a later date.
I have fitted guttering to both long sides. The water from same is ducted to a nearby drain. The roof is a peaked: no guttering is attached to those ends of the shed. The roof covering is traditional gritted felt. The walls of the shed are the 'log cabin' style, T & G. Externally, they have been painted with traditional water-based, water-repellent paint. Two non-opening, single-glazed windows are fitted.
The location of this shed is such that it is well-screened from high winds.
The overall height of the shed was limited by planning stipulations of the local authority. It has yet to be 'inspected' by the powers-that-be . . . and I'm not anticipating that that event will ever materialize.

Al.

[David Simpson]

Al, your shed is definitely not a DIY store cheapo shed. You've ticked all the boxes & it'll last a lifetime. Well done.
Lawrence's shed looks of permanent habitable quality - fantastic.
Outdoor wise, I've a decent old caravan, which thankfully is weather tight, not damp, and has electric heating if required. Its just used for radio/electronics storage & occasional minor work. My main r/el work is done inside - in a wee well ventilated 6' x 10' workshop/office/freezer - storage room.
Reason for banging-on about timber framing, vapour barriers, etc. :- prior to leaving the RAF - did a two year D/Rel. ONC course at a college, for surveying & building technicians. With a view to designing my own timber-framed house & building it. Which I did. Back then, in the mid 70's, decent Scandinavian & Canadian off-saw white wood could be bought relatively cheaply & readily available. The w/w o/s bought these days in DIY stores, and even builder's merchants, is often home grown. Often displaying shakes, loose knots, and a tendency to bowing(banana shape). And jolly expensive, compared to years past. Worth paying a bit extra for well treated CLS, compared to O/S. Jesus - what a price dressed timber is nowadays, particularly redwood. Got my hands on a handful old ex distillery roof timbers a few years back - effing pitch pine(rocking-horse manure). But that's another story.

Regards, David

[Skywave]

Thank you, David. I did look at ready-made sheds in various D-I-Y stores, but apart from the type and quality of their construction, what forced me to go in for the one I have was simply to make maximum use of the available space outside. So a bespoke approach was necessary - and, surprise, surprise, it wasn't cheap!

Anyway, all that as it may be: to return to things more relevant. Based on what I have read here (and elsewhere), my understanding of what needs to be done for thermal insulation is best described by a drawing: one is attached.
The studding sets the amount of horizontal space available: 45 mm. Assuming that the thickness of the vapour barrier is negligible, there is obviously a trade-off between the thickness of the insulating material and the free space. And that itself assumes that a suitable thickness if the insulation is available. Since 50 mm. thickness is a common - but not the only thickness - available, it may be necessary to add thin battens to all the studding to increase that 45 mm. Obviously, I'd prefer to avoid doing that. OTOH, I have no idea how wide the 'free space' should be. Also of note is the fact that the horizontal spaces between much of the studding is not of a constant dimension. That could also impact on my choice of insulating material.

So a few Qs. & possible problems arising in that last para.: helpful & relevant remarks would be welcome. In particular, does my drawing illustrate that I now have the right idea?

Al.

[ms660]

Al, is there any lining membrane between the inside face of the external cladding and the external face of the studs?

Lawrence.

[Skywave]

Lawrence: thanks for your reply. The answer is no.

Which, after noticing that absence and in retrospect, it surprised me, since I have a small, wooden garden tool shed (bespoke built, locally) in the back garden which has something so fitted that seems to meet your description.

I deduce that suchlike fitted to the walls of the shed under discussion would be desirable, but, alas, I cannot do that retrospectively. However, will its absence cause a significant problem and, moreover, if it will, what can be done about it now?

Al.

[Station X]

A bespoke shed which I purchased more then 30 years ago had something called "building paper" in that position.

[Tractionist]

Mmmm ..... 'Sisalkraft' - great stuff!

[ms660]

The sheds I used to make and sell had the stud frames lined with Tyvek or similar, 2"x2" studs for anything up to and including 8'x6' shed, that was a real 2"x2" too, I had control over the finished dimensions as I used to mill homegrown timber straight from the log, any larger than 8'x6' and the stud depth increased in proportion, shiplap cladding was to order, standard cladding was 5" feather edge board which I cut, usually from Larch or Douglas Fir, boards fitted with a 1" overlap, all pressure treated for an extra cost.

For Al's I would make sure the outside doesn't leak to the inside via cracks, loose or missing dead knots, porosity, poor joints etc then fit 30mm foil backed insulation such as Kingspan or similar in between the studs, flush to the inside face of the studs, then counter batten with 50x25mm and infill with 25mm foil backed insulation then vertical batten with 50x25mm battens at centres to suit a wall board material and run any electrics down the gap, easy to fit flush sockets too if at least a 12mm thick wall board is fitted, probably get away without a vapour barrier if the insulation joints are properly taped/siliconed etc.

Lawrence.

[Philips210]

Originally Posted by G6Tanuki

Nice in theory, but I did that on my summerhouse roof a while back, and the channels between the coroline and the underlying ply were promptly occupied by a range of small forest-rodents.

Hi

I am at the stage where I need to replace the roof on my small workshop and have been pondering on what to use.
The original heavy duty felt lasted many years before leaks started to occur. A subsequent further recover of the shed felt lasted a few more years but I have now little confidence in using felt. One thing against felt and any dark coloured covering is that it attracts the sun's rays so can become quite hot inside during the summer months.
I had considered using Onduline which I understand you still need to first line the roof board whether its OSB (sterling board) or plywood. Again, it's generally dark coloured which I guess could be painted with a lighter coloured finish.
Something else I've also been wondering about is corrugated fibre cement sheets. These look a little like the old asbestos sheets and being light coloured should keep the inside generallly cooler than other finishes and last for ages. Farm outbuildings often use this type of roofing. Has anyone had good experience of using this type of covering for a workshop?

Regards
Symon.

EDIT: Just noticed Lawrence's mention of the fibre cement corrugated sheets in post #24. Looks very impressive.

[nutteronthebus]

Hi

I am at the stage where I need to replace the roof on my small workshop and have been pondering on what to use.
The original heavy duty felt lasted many years before leaks started to occur. A subsequent further recover of the shed felt lasted a few more years but I have now little confidence in using felt. One thing against felt and any dark coloured covering is that it attracts the sun's rays so can become quite hot inside during the summer months.
I had considered using Onduline which I understand you still need to first line the roof board whether its OSB (sterling board) or plywood. Again, it's generally dark coloured which I guess could be painted with a lighter coloured finish.
Something else I've also been wondering about is corrugated fibre cement sheets. These look a little like the old asbestos sheets and being light coloured should keep the inside generallly cooler than other finishes and last for ages. Farm outbuildings often use this type of roofing. Has anyone had good experience of using this type of covering for a workshop?

Regards
Symon.

EDIT: Just noticed Lawrence's mention of the fibre cement corrugated sheets in post #24. Looks very impressive.[/QUOTE]

I use Bushbury steel there Plastic Coated · 20-30 year life span in various colours on my shed , garage and patio cover ( see post #13 )

[The Philpott]

I have just seen a couple of single garages being re-roofed with the modern corrugated cement sheets, there were no complaints from the men who were doing the job as regards ease of fitting..but they were, as you'd expect, expensive. I don't imagine any problems will reveal until they start to age..

[M0FYA Andy]

For my workshop I used box-profile steel cladding from this firm -
https://www.roofingsheetsbyrhino.com/
The steel is galvanised and then plastic-coated.
I've been totally happy with the results.
Andy

[nutteronthebus]

this is the side of my shed with roof showing

[ms660]

The cement fibre roofing sheets I used were Eternit Profile 3, with all the ones I've fitted they were fixed with SS coach screws with small SS washers and spats, single tier is no problem, for two tier etc you'll need to mitre the joints to avoid four sheet thicknesses on the side lap, it's not difficult to do, you can use a cutting disc in a bog standard angle grinder or even a sacrificial hard point hand saw, it's also important to get the first one laid square to avoid run out at the eaves and the ridge, to allow for thermal movement the fixing holes need to be a couple of mm or so larger than the fixing's diameter, for mitres make sure there's a 3mm or so gap at the joint.

Lawrence.