Hi everyone,

We always intended our build to have an oak-framed porch and matching fascia. Also, we hope to leave the timber untreated so it 'silvers' over time. We therefore need to use green oak as kiln dried would just readjust to atmospheric moisture levels (aka wet) - correct? I'm relatively confident about the porch anyway as we'll likely have this at least machined by a professional...

My main query is around what to use for the fascias - if we use totally green oak, will it shrink, and if so, is there a method we can use to stop it twisting my rafters as it shrinks? Finish is stone skin walls. This is also complicated by the need for a ventilated soffit! Should we use another kind of timber? The plan is to have the fascia and porches matching...

Also, does anyone a sawmill in the Durham area with a good reputation for supplying very durable timber?

Never seen one of those before David - it could make things a lot easier. We've a semi warm roof with insulation between and underneath the rafters and a gap between the insulation and the membrane. Are they ok in an exposed environment or might we see runoff being blown back through the ventilation? Apologies if I haven't quite grasped how they're fitted.

Posted By: JamsterWe've a semi warm roof with insulation between and underneath the rafters and a gap between the insulation and the membrane.

I would always recommend using a breather membrane & putting the ventilated gap between the membrane & the tiles/roof covering. You can put the ventilated gap between the insulation & the membrane, but this doesn't take advantage of the membrane's breathability & encourages thermal bypass, i.e. where wind bypasses the insulation leading to increased heat loss. I imagine it would also increase the risk of run-off being blown back under the membrane, but I've not heard of this happening in practice.

If the ventilated gap is above the membrane then the over-fascia vent fits on top of the membrane. If the ventilated gap is below the membrane then the over-fascia vent fits below the membrane. In either case it is mechanically fixed to the top of the fascia.

If you're using breather membrane then this shouldn't be left exposed to sunlight. So the first run of membrane is normally replaced with something more substantial, e.g. an eaves protector, an eaves carrier or a type 5U eaves sheet. This would limit the extent to which run-off could blow back under the membrane.

David

Second the Kiln dried option, although finding some air dried may no be too difficult in 1 inch or so thick (1 year to dry).
Problems you will get though by leaving the timber to silver as you put it, would be in a timber only an inch thick and say 7 inches wide with no protection would be subject to "dimension instability".
The rate in which the timber takes in and sheds moisture, have solar gain/drying on outside face and not inside will result in cupping, twisting and splitting.
There are obviously coatings you can use to make the Oak more stable but if it was me I would use a more stable Hardwood and coat it in a contrasting solid opaque colour of a F and B Gray or Black shade for instance.
A water based product like Jotun Denidekk with their Visar primer for instance could give you 8 - 10 years protection. And a nice contrast against the more rustic chunky sections of Green Oak?