Quite often a cut timber roof is used for a room where the ceiling height will be restricted, for example over a garage.
In this case the joists won't run between the wall plates, but will have to be collar ties. Purlins are also usually used to support the rafters, and this will tend to stop them spreading. The final part in this is where the ends of the rafters are skew nailed to the wall plates or fixed to the wall plates with truss clips. And, before that, the wall plates are tied down to the walls with galvanised straps and, optionally, fixed to the walls with frame fixings or hammer fixings.
See the Hints & Tips section for more information.
Next, check for a leak in the roof - this may require a professional roofer to check the slates / tiles, ridge tiles and valleys, flashings etc. We have seen a roof "suddenly" spring a leak in the lead valley - how did the valley suddenly get punctured? Well it didn't. It was punctured several years ago by some hamfisted roofer who was replacing some slates, dropping some onto the lead valley. The underlying old bitumen based roof felt eventually cracked through the effects of heat, as does all such roof felt and, bingo, the considerable amount of water coming down the valley then drip drip dripped through the hole and roof felt.The worst scenario could be that the water is penetrating the chimney stack. A badly built stack, or a stack on an old house, will allow rain to pentrate directly through the roof and into the supporting chimney breast. If so, the stack must be rebuilt - see our page in the Hints & Tips section on Building a chimney stack.
You will need to stick the sheets together otherwise the concrete will get between the sheets and bang goes the barrier against water ingress.
The DPM is brought up and over the blocks of the inner leaf. The DPC (100mm wide) is then laid over the top. The two membranes do not need sticking together here - the weight of the blocks will ensure a good contact and prevent water from seeping above the Damp Proof Course.Surfaces must be clean and dry. Adjacent sheets must be overlapped by a minimum of 150mm. Visqueen Double Sided Jointing Tape should be used to join adjacent DPM sheets. The sheets should then be sealed by using 100mm wide Visqueen Girth Jointing Tape. Where the sheets have been perforated they should be patched with sheets of identical thickness lapped at least 150mm beyond the limits of the puncture and sealed with Visqueen Double Sided Jointing Tape and Visqueen Girth Jointing Tape as per standard lapping instructions above.