I am in the process of preparing plans for an extension to my house. I would like to incorporate a green oak “cruck” frame within the kitchen and extending on upwards to give a vaulted ceiling within the bedroom above. I would like to fit the frame against the inner leaf of a blockwork cavity wall.
I was wondering whether there would be any problem with positioning the frame here i.e. would there likely to be much axial movement of the posts as the oak dries, which might cause problems with the blockwork internal skin adjacent to the post. How far would you suggest the posts should be set away from this skin?

Thanks Steve.

to some degree, movement may be tied to the quality of the timbers and the joinery. good quality timbers would be more stable, especially where twist is concerned, and tight joins would help keep things in place also.

how thick is the block wall and what does "inner leaf" mean?

The blocks/masonary are made of dense concrete and are 4 inches thick. The concrete blocks are built as 2 seperate skins with a 3" inch cavity/void between them (partially filled with an insulation board), the 2 skins are tied together with steel ties built into the mortar joints between the blocks. The "Inner leaf/skin" is the internal block wall. As you can see this build uses both traditional block/masonary type construction along side the even older timber framing.There are many timber framing companies emerging in the u.k. (Timber framing is becoming very popular again) which are now carrying out this type of build, that is - mixing "old" with "new" But these companies are not very free with their advice!
Back to the original post - The Oak I am using is a good quality French Oak I have seen the tree trunks and they look reasonably straight (still with bark on) but as i am inexperienced in framing I wonder if there may be any movement As the frame dries which might damage or even push the block wall. The posts are 10" by 8" I was thinking of leaving a gap of 1/2 inch between the posts and the block inner skin, do you think this would be enough?

recall basic timber drying shrinkage. The wood shrinks in cross section as it dries. The length of the timber will shrink very little.

Hi Greener,

Your problem is not really related to the drying and shrinkage of the timber but more to do with the practicalities of raising the frame and driving the pegs. Since most pegs are driven from the outside of a frame then your block wall will probably be in the way.

The second major consideration that would affect movement is dynamic loads. Timber frames are really quite flexible with analysis models predicting up to 25mm of movement in high winds.

If you send me a copy of your cruck drawing then I can help you further.

Ken Hume

Contact details http://www.kfhume.freeserve.co.uk