Porch build

[Froggy]

Hi everyone, I'm planning on building a porch very similar to the one in the picture. But I have a couple of questions before I start. First is the wood choice, I'm using oak and was going to use dry oak but a lot of builders seem to use green oak. I can understand that from a financial point of view but surely the oak will move too much as it dries out? Next question is about attaching the wooden frame to the breeze block base. What's the best way to do this please? Any other advice would be welcome.

T.I.A. guys.

 

[MikeG.]

I did a detailed work-in-progress type posting here a few months back of my own oak porch build. All of your questions are answered in that, so have a look here.

There's a very good reason that oak framing through history has been done with green rather than seasoned oak: green oak is workable! Seasoned oak is too hard to sensibly make deep mortices. The joints are big and robust, and the pegs hold everything together well.....and the fact is, it's outside, so although it will dry and shrink a bit, it won't be to the same extent as internally. Almost all British historical framing was done with green timber.

Straps on the underside of the sole plate, dressed down over the inside face of the masonry and screwed & plugged......that's the best way of holding everything in place.

 

[Froggy]

Thanks Mike, I'll have look at the link. Nice porch, if mine turns out half as good I'll be happy.

 

[Sgian Dubh]

I have a couple of questions before I start. First is the wood choice, I'm using oak and was going to use dry oak but a lot of builders seem to use green oak. T.I.A. guys.

One reason you can't get 'dry' oak is that no-one (kiln) dries large oak beams or sleepers. It's not cost effective and liable to failures or drying faults of one sort or another, so the nearest to 'dry' you can get is air dried which, at the core, is still likely to be pretty wet. e.g., 30%+ MC even after many months and even years. Large oak sections are frequently used in traditional heavy timber framed building types, e.g., porches, sheds, barns, houses, restoration of architecturally important buildings etc, and eventually the wood will dry out to suit the typical seasonal relative humidity range it experiences, as well as normally splitting a significant amount.

Interestingly, this type of wood used in buildings gets stronger over time as it dries. This means that buildings built with enough strength to cope with the stresses the load imposes using 'wet' wood become significantly overbuilt as the wood dries. If I recall it correctly off the top of my head wet wood can only carry about 60% of the load an equivalent dry piece of the same species and dimensions can carry, and builders have to use the 'wet' load carrying capacity to ensure the building is strong enough when new. Slainte.

 

[Froggy]

Thank you Slainte.
Mike, great WIP thank you. It will be very helpful I'm sure. Just two questions: firstly what is the v groove for that you made in the soul plate at the very beginning of your WIP and secondly what was the thickness of the beams in the main part of the frame?

 

[MikeG.]

The groove on the underside of the sole plate was A/ to give the mortar bed something to grip on, and B/ to form an upstand in the mortar bed which would mean that even in the event of twisting up of the sole plate there wouldn't be a straight path through from outside to inside. Everything about designing in green oak, from the design of the joints to the profiles you cut in posts and plates is all about allowing for shrinkage and movement.

The posts are 125 square, the sole plate ex 150 x 150, and the wall plate 150(D) x 125(H). The corner posts and door posts are 125x125.

 

[Froggy]

Thank you Mike, much appreciated.