Cupressus lusitanica

Case Study

The long term performance of all solid wood building components using Cupressus lusitanica is vital knowledge. Documentation of this performance is largely absent. We have a unique opportunity to add to this knowledge and we do so here as a Case Study based on a house we built some 40 years ago that has all its solid wood components built from C. lusitanica.

The house is four bedroom, two storey built on a concrete pad and has a colour steel roof. C. lusitanica is untreated and much of the timber is rough sawn. The house met all compliance requirements which is largely dependent on Heartwood and visual grading criteria. In the following table we describe the solid wood components its performance over the 40 years and remedial work required or carried out.

The timber came from a high pruned C. lusitanica stand. We don’t have planting date or pruning and thinning dates. Logs were provided in 1986 and after sawing we ‘air’ dried the timber. The house, designed by a Rotorua architect Gerald Stock was built by Master Builder Don Parkes in 1987.

25 to 50mm thick timber is generally provided at a nominal 16% moisture content.

Component	Timber	Current Condition	Maintenance

Cladding (Natural sawn surface)	200*25mm board and 75mm batten, No surface coating, RS, HW & K.	Grey weathered. Minor degrade with ground contact, minor splitting and checking	Nil to date. No immediate work required.
Exterior Weather protection	75*25mm RS, No surface coating. RS, HW & K.	Grey weathered, Good	Nil
Facia	200*40mm Planed, painted	Good	Colour changed
Exterior Doors	Stiles and Rails 50mm 150 and 200mm. HW,clear Glass panels. Exterior painted. Interior oil.	Good	Colour changed
Interior Doors	Stiles and Rails 50mm 150 and 200mm. Wooden panelling. Polyurethane, oils	HW and SW. Excellent condition	Nil
Architraves, skirting, general moulding	Various, Polyurethane, oils	HW and SW. Excellent condition	Nil
Beams	Some 300*90mm, Polyurethane, oils	HW and SW. Excellent condition	Nil
Panelling and Sarking	Ex 150*25mm moulded, Polyurethane, oils	HW and SW. Excellent condition	Nil
Doors & windows liners and mouldings	Ex 150*25mm moulded, Polyurethane, oils	HW and SW. Excellent condition	Nil

(WB weather board; RS is rough sawn; B & B board and batten cladding, HW is heartwood, SW is sapwood, K is knottygrade)

Surface Coating

Cupressus lusitanica used externally either as ‘rough sawn’ or machined timber can be left to weather naturally. As such it will weather naturally to a silver grey over one to several years. Weathering may mean some surface mould develops but this will depend on the local climate and it can be removed with a ‘wash’ liquid. Leaving the surface to weather is a matter of taste and convenience.

Coating. There are many good oil and stain products available. Such coatings may extend the life of the timber but sufficiently dry timber that meets the required grade will behave very adequately. (In the Case Study house the rough sawn untreated cladding timber has been mostly fit for purpose for 40 years.)

Brush on products are available to clean mould and also to stain and oil the timber surface to taste. You may choose to order pre-coated timber (sides and ends). Manufacturers recommend a second coat within around 3 months and the third coat in around 18 months. Thereafter a coating should be applied within around a 5 year period.

We have been impressed with the products of the Natural House Company. See www.naturalhouse.co.nz for product list for both external and internal coating oils and stains and for general information.