The Workshop Construction: External Cladding

PART 6: Timber and rear cladding

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The cladding is Douglas fir from a local saw mill (English Woodlands). The planks are 8″x0.8″, sawn, and work out at about  £13 per m². Douglas fir is one of our cheapest UK grown timbers yet has many characteristics that make it superior to standard softwood. UK grown Douglas fir is classed as only slightly durable – apparently our weather makes it grow too quickly, hence it is often recommended that it is preservative treated, but this is not necessary if the design and detailing are good. An excellent example of untreated Douglas fir external cladding can be found in the ecological building of the Scottish Renewable Energy Office for Natural Energy.

Design features to ensure longevity of the cladding:

  • Ventilation is provided behind the boards by fixing them to tile battens. An air gap is left at the top and bottom of the cladding so that air can flow freely behind them
  • Water repellent stain keeps moisture from penetrating the wood – OSMO One Coat Only ebony stain is highly water repellant and was applied on all edges before installing, and on the front and back of the overlapping sections as these will be impossible to paint later. The end grain received additional attention.
  • Stainless steel screws prevent rusting. Note that the screws on one board are not covered by the board above, so it is possible to replace a board without having to remove those above or below. Screws were pre-drilled to reduce splitting.
  • End stops terminate each run, reducing exposure of the vulnerable end grain.
  • Roof water is carefully directed away from the cladding via downpipes so that water does not cascade down the boards. Good overhanging eaves help too.

The above detailing should ensure a very long life – in excess of 30 years I trust. Maintenance will consist of replacing any cracked boards and occasional touching up of the stain. Re-staining is easy with OSMO One Coat Only – it does not peel or flake and you can just put another coat straight over the top at any point.

Back of the building

As the back of the building is rarely seen and difficult to access for repairs I have used a maintenance free cladding – Coroline bitumen corrugated sheets. These were fixed with screws and special rubber/stainless steel washers to the tile battens. They overlap to ensure they are water proof. They are certainly not lookers, but they should never need painting!

The finished building

Here is the finished building… well, almost finished.  The cladding and colour help it fit in with the other garden buildings, and it is a damn sight better looking and better constructed than the tumble-down sheds it is replacing!

«The Green Roof | The Workshop: 1 2 3 4 5 6 | Surrounding Landscaping»

Find out more about the surrounding landscaping here»

33 thoughts on “The Workshop Construction: External Cladding”

  1. Excellent blog, we are thinking of building something very similar in our garden. We will certainly be using your blog as inspiration. The green roof and external cladding looks brilliant. Thanks for the info.

  2. Just stumbled across your garden building project. Coincidentally, I have just finalised the design for my garden studio/workshop which is similar in most respects. Your problems will be my problems and it’s reassuring to see how you approached them and solved any issues. I have to do most of this work myself because of cost, so thanks for the inspiration!


  3. I am currently planning my garden office. 14′ x 10′ – The only area I’m unsure about is the joist to use for the roof. Always at the fore front of my design is the 2.5m height limit. I’d like to use 4 x 2’s with firring strips but will these be ok for a span of 10′ ?

    • Hi Peter,

      It depends on the roof materials. If it’s ply and felt – no problems, but if you want to support a green roof, then that would be insufficient. As my experience showed, I needed to reinforce my 4x2s with steel plates screwed onto the side of each joist to stop my roof sagging.

      If you are not planning a green roof then consider that 4×2 is the standard size for ceiling joists in houses where there is an attic space above, and those can span rooms much wider than 10′. Many people lay a loft floor straight onto that and the ceiling below does not sag appreciably. Remember you can always place joists closer together, although that is not as effective as using deeper joists in the first place.

      • Hi Keir,

        Thanks for the prompt reply, it’s settled my mind now and I can crack on with ordering the wood. Now that it’s some time since you built your workshop, how do you find working in it? Does it retain heat well and are there any things you would change in it’s construction if you could?

        • I’m really pleased with this building – it’s nearly up to habitation specs, so feels like a permanent building. I only heat it as and when I work in it, and a fan heater is all that is needed in the winter to keep it cosy. Compared to a normal shed, this building is virtually insect and spider-free, as it is so well sealed.

          One end has a couple of freezers in it – I purchased ones that work with low temp environment.

          The green roof keeps the whole building cool in the summer too – if you are going for a light weight roof (ply and felt) you will probably find it very hot in mid summer.

  4. Hi Keir.

    I’ve now completed my listing of what materials I will need and the cost is going to be in the region of £900 to £1,000. I’m going for the EPDM roof.
    I am considering whether I should go for Tanalised wood for the wall framing. As I’m sheathing with 12mm OSB3 and breather membrane, I’m so not sure if it’s worth the extra cost or even required.

    Is there a reason you chose nominal 2×3 regularised over CLS and was it Tanalised?

    • Can’t remember for sure, but I think that I used tanalised wood for most of it. On reflection the building is so water tight that I probably didn’t need to, but it does give me a sense of security.

      On another garden building (the cabin) the cladding was screwed straight into the framing and water did track along the screws making the framing wet when the rain was particularly persistent. In the case of the Workshop the cladding was screwed into battens, so there is no direct path for water to take. That said, the battens will become damp after rain, and where they are screwed to the framing there is a (small) chance of some water tracking along screws into the frame. My experience of pulling down old sheds is that rotting sets in first around screws.

      I would definitely use tanalised for the base plates (where the wall panels sit on the concrete base), and would suggest tanalised framing above this is probably worth while, if not entirely necessary, as its a relatively small additional cost for the increased peace of mind.

      BTW I’d love to see a picture of your project when it’s done!

  5. Hi keir,
    Nice little project this, can you give a rough guide to sca, ing this out in MS word. Also what was the appx total cost for you?

    • Hi Danny-boy. Sorry I missed your comment – just seen it now. I expect my reply is too late, but anyway…

      In MS word, insert new drawing canvas, then on the drawing tab select arrange/grid settings. You can set a grid to 1 mm x 1 mm so everything is to scale. Choose snap to grid, rather than snap to object, so your lines and shapes stay on the grid exactly. I usually choose to ‘show lines’ every 10 grid spaces to give a 1cm visible grid.

      As for the cost, I’m afraid I can’t remember and material prices have increased since I built it anyway. Suffice it to say, it cost a fraction (20% ?) of what you would pay if you had it done by a garden building company. I reckon it came in under £4000 but don’t quote me on that!

      • Thanks Keir.
        Not too late at all! A good idea is a good idea no!?
        I’m still mulling things over til summer warmth kicks in.
        Thanks for the tips.

    • Hi, thanks for stopping by.

      From what I can remember, I think I dropped a total of a half dozen screws through the wall base into the concrete, but these were just 4inch screws into standard plugs, nothing special. They were primarily to prevent the walls moving during construction. A bit more detail: Once I had the wall panels up but before I started on the roof, it was possible to shift them a few cm each way, which was necessary to get everything square and straight, however, once one side was good it would shift out of line as I squared up another section – hence the use of a few screws to stop it moving. Once the floor and roof was installed there was little chance of the walls moving, screws or not!

      • Great. Thanks for the reply.
        Not having tried this scale of construction before I had visions of s high wind blowing things down! But I guess the weight of roof and strengthening of panels keeps it all in place.

  6. Hello Keir,
    Do you have a diagram/sketch of the wall corner detail that you could post?
    I am not quite clear how the corner is formed so that it all looks right from outside.

  7. Hi there, thanks for taking the time to put up your project. I’m building a very similar project but with a much longer fall (5.6m) for the flat roof, so will too struggle with the permitted development issues with regard to head height!. I wondered if you have any detailing of what you did with the internal insulation and over boarding? I’ve been debating kingspan sheet insulation, but you mentioned sheep wool insulation and wanted to know how you installed it and then finished the inside. Cheers!

    • Hi Mat, thanks for stopping by. The insulation in my roof and walls is wool and recycled plastic bottle – spun material that comes in rolls and is about 3inches thick. I simply pushed it in between stud work (in the walls) and between rafters (in the roof). I used some offcuts of tile baton as mini noggins to stop it falling down. Kingspan or similar solid insulation is fine too – I’ve used that in one of my other garden buildings (‘The Cabin’). I preferred the wool as the dust from cutting the kingpin is pretty unpleasant, and I find it hard to cut exactly, so the gaps then need filling with mastic. The wool / spun plastic was so easy to use – I could tear it with my hands, and unlike rock wool there was no skin irritation. The internal boarding was all done with MDF sheets. I routed v groves every ft or so, so it looked like wide planks. The join between the boards just looked like another v-grove. MDF paints well too. Hope that helps. Good luck!

  8. Hi, great project, it’s certainly given me food for thought. I have a useless triangular piece of land behind my garage that I’d like to turn into a brewery / hobby shed. I had initially thought of a block construction but seeing the build quality and flexibility offered by the timber construction, plus the reduction in cost and I think I’m likely to go this way. We live rural and see lots of wildlife, some less desirable, do you think the construction us rat/squirrel proof?

    • Hi Ian, thanks for stopping by. Re: rat proof, yes, pretty well, although rats can chew through timber if they are desperate. All I can say is that I had rat problems in my previous shed, but the workshop is rat (and spider!) free. The construction has no voids or access spaces that would allow rats or squirrels entry. BTW the building looks pretty muck as good today as the day it was built (bar the white paint needing redoing) – it has really stood the test of time. Good luck with your project.

  9. Hi, really found your blog very helpful. I am well into my build now which is in a 7.5m x 4m swimming pool which is built into a slope. I have layer one run of blocks around the top of the pool edge and used your method of building my panels which are the width of one sheet of OSB high, 1.220m then I have put 7″x2″ joists on top at 400mm centres and a fairing piece on top of that to give the fall I need. Then 18mm OSB will go on top. Reclaimed double glazed units will be built into the front on the down slope once I have dug the soil away to the door level. Should make a great workshop for me to do my woodwork. I am hoping to put a green roof on once I can afford it. So, thanks for all the inspiration and detail in your blog which I found to be the best. Regard. Andy

  10. Hello, we are just about to cladd our garden studio ourselfs. Just noticed you lovely site. Do you think it’s ok to use 8″x1″ tanalised boards instead of the douglas fir? I would paint it with osmo natural oil stain. The vertical battens are 400 mm apart….do I have to screw through into every batten 2 screws? It is all a bit confusing as you read different things all the time.
    Many thanks Birgit

    • Hi Birgit, sure, tantalised boards will do. If I understand your question correctly, then yes, you need two or three screws per board into each batten to stop the board cupping. Because each board overlaps the one below it some screws may need to go through two boards to reach the baton, making three screws per board, which is what I think mine ended up being. If that’s not clear let me know and I’ll post a diagram to clarify. The OSMO stains are great. Can’t recommend them highly enough. The only downside I have found is algae growth on the shady side of the building as the OSMO stains don’t contain biocides.

      • Thanks Keir for the quick response.
        Did you use feather edge? The timber store tells me that would be better, but I’m not sure. Have you had to repaint the ebony by now.

        • Mine were not feather edge, just regular boards and they worked perfectly. Feather edge can look neater, but you are getting thinner wood at the tapered edge which is potentially more prone to decay just where the drips from the board above fall. But I really don’t think there is much in it, so take your pick. I have repainted the boards once or twice in over ten years. It’s not so much that they really needed it, but it makes the whole thing look like new. The stain lasts longest on rough sawn wood rather whereas it gradually erodes on planed wood such as windows, especially horizontal surfaces such as window cells and door thresholds. These need redoing every few years.

  11. Awesome. I have a 36ft x 14ft area at my rear boundary that requires something extremely similar!…. minus the green roof because I already have a large area to upkeep, and my neighbours wont be happy at the right of the construction due to my land being quite a lot higher.
    My neighbour would not be happy seeing me up on the roof overlooking their garden with a weed sprayer considering that is the one that screams, rants, bashes the rotating washing line around with a bat if anyone has a fire within 30 meters…. I trust (certainly hope) your neighbours are normal, happy people really thankful for the green roof though.


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