shiplap question

15 Jul 2007
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United Kingdom
Im cladding my new summerhouse with 110 x12 mm softwood tprereated tongue and grooved shiplap

the shiplap has been stored outside for a week during the warm weather and seems quite dry

Do I fit the shiplap tight or leave a small gap in the tongue and groove

As some of the shiplap has cupped already I was going to fix it by means of one screw in the middle of each board

Does this seem ok

When cutting and fixing the shiplap should I treat the bare cut edges

Whats the best detail on the corners

The shiplap is being fixed on vertically fixed treated battens fitted to stirling board panels
The stirling boards are clad with breathable membrane fabric

Do I need to seal off the gaps between the vertical battens
Or just leave them open to ventilate the rear of the shiplap

Along the front edge of the summer house I intend to bolt a new decking joist to the summer house joist so I can erect an external decked area

How do I finish off the shiplap at the junction of shed and decking to avoid problems with rain water


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1) you have to leave a gap. Try a matchstick between them when they are dry, as you screw them to the wall. Pull the matchstick out when fixed. They will expand this much when damp. If you have any spares, throw away the most cupped boards.

2) A single screw in the middle of the board is correct. If you put one near the top and one near the bottom, it will split between them. You can conveniently drill the holes in the boards to suit your battens, before fixing them. However, they will need several screws along their length - at batten intervals of 450 to 600 mm

3) You must treat the cut edges

4) The ends need extra protection from the weather. I used teak strips which my local supplier happened to have, and screwed them into the end battens, tight against the ends of the shiplap. You will probably not be so lucky. Any vertical strips should have the ends soaked in preservative as they will tend to rot. I cut and drilled all my shiplap prior to fitting, and this enabled me to treat them on all edges with the water-repellent stain before fitting (extra coats on end grain)

5) leave the backs ventilated, as rain will get moisture behind the shiplap. It is probably worth treating the battens too.

6) at the bottom, kick out the lowest piece (e.g. with a small wedge) to throw water out and away from the battens (the batten need not go right to the bottom) and stop the shiplap an inch or more above the decking. the bottom one will rot first, so cut and prepare a few spares. I tucked my spares behind the cladding ready for future use. In my case I have a dwarf brick wall at the bottom of the cladding, so did not have the same problem. but you want the water to drip off without splashing up and without having a pool or wet surface that the cladding stands in.

Here's mine:

Big-All's shed is splendid, i suspect he hasn't got a house ;)
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JohnD said:
Big-All's shed is splendid, i suspect he hasn't got a house ;)

us boys need to "escape " occasionaly :D :D :D

theres a phone a telly and a cool box in there
and what ever you do dont drink the "cider "from the plastic bottles ESPECIALY if it feels warm :D
he he my new shed is a 25m x 4m stable block ive just had re-roofed on a hill overlooking shoreham. Im moving all my kit up there with running water and electric. Wife thinks its for the storage for the business etc.....he he he! :LOL:
Thx all

Great advice and much appreciated

If i fit the t&g tight with one screw in middle when boards are dry are they likely to split when they get wet

If I use a matchstick spacer isnt there a chance the tongue may shrink out of the groove

Ill upload some photos soon of my shed build

Can any one reccommend a free hosting site for my photos


measure the actual size of your boards if they are 112 great whack em tight as they have 2mm to shrink so no spacing required :D

if you screw a cupped board near the top or bottom you will have to pull a bit more on one edge as it will be sticking out more

when i reclad my shed after some board sprung out the grooves i left a 2mm gap without being accutate and its fine now
knocked together gap lookes 2mm screw together

also avoid the last 2" of the boards to prevent splitting
what i have done is angle the screws in at 2 1/4 from the edge so they just come in at the corner and dont drive home to much to avoid splitting ;)

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