I have a 4 year old timber frame house. Spruce and aspen were used for the timbers. About 1/2 of the timbers have some degree of checking and some are big enough to stick your finger into. I have a couple questions:

1. Can checking be bad enough to cause structural problems ?
2. Can entire timbers be replaced ?
3. Are there any cosmetic solutions - flexable chalking or some way of clamping and banding the wood ?
4. Are spruce and aspen appropriate materials.

Thanks for any help.

PJ

Checking may reduce the strength of the timber depending on the location of the openings.
1. Large checks at or near connections are probably not good, as they may reduce the shear capacity of the remaining wood and the connection.
2. Checking typically does not affect stiffness or bending strength since the wood fibers are not fractured, but merely separated (you could pull apart the multiple strands of a cable, but it wouldn't break any sooner). Therefore checks away from the connections shouldn't cause the timber to bend or break at loads less than those for which it was designed.

Dear PJ,

You don't say which timber is checking more than the other i.e. spruce or aspen.
What type of conversion has typically been made to each timber that is checking i.e. boxed heart, halved, quartered, slabbed, etc.

I suspect that boxed heart aspen would be the most prone to checking being faster growing and having a higher water content than spruce.

Checking is not a particularily good feature in a timber because it can introduce planes of weakness, particularily when spiral grain is present. The lines of fibres mentioned above can be broken when for example a line of joist pockets are cut into a summer beam or wall / sill plate and then the timbers have a tendancy to open up more than they should with the joist or wall studs acting as torsion bars on the timber helping to open it up. There is no cure for spiral grain and this type of timber is best consigned to the bone yard or used for "non structural" elements e.g. wall studs.

Where you do not want checking then quartered conversion is best but you will then replace checking with cross sectional diamond distortion as the timber dries.

The best solution that I have seen to date is to slab halve convert timbers and then to dry, plane and glue them back together again as a two ply beam where the beam now has two outside heart faces. This type of timber is remarkably stable and check free.

See the Finland 2001 article on my website for more details. http://www.clik.to/WorldofWood

Ken Hume