WALL CLADDING

Introduction

 This structure of this timber framed porch extension was constructed some time ago but the weather proof cladding was not completed, leaving the structure exposed to the elements. The aim of the project was to provide an weatherproof finish to the structure that was durable, attractive and economically viable. Pre-painted cement board cladding was chosen, it is relatively inexpensive and weather resistant, its main weakness being vulnerable to impact damage that is difficult to repair.
Initial Inspection

The first step was to strip off the incompleted cladding to expose all the structural elements for a thorough inspection to see that their exposure to the weather had not reduced their strength and so be unable to perform their function adequately.
 The roof had sagged slightly due to a number of roof support beams losing their strength from exposure to dampness and so needed to be replaced. Apart from that most of the weathering was purely cosmetic, would not effect the structural stability and would be covered by the cladding.
 Fortunately, polystyrene boards had been used for insulation between the framing timbers which is fairly weather resistant and although exposed to the elements, survived with minimal damage.


    

Repair/Complete Insulation
Large missing areas of polystyrene board were filled with the same with smaller areas and gaps around the tiles being filled with freeze-resistant foam, providing  an effective barrier against the cold.
Apply Building Paper

To provide an effective barrier against external moisture, whilst at the same time allowing internal moisture to escape (so that it will not  get trapped in the wall structure and cause rot), a layer of building paper was applied to the entire wall surface area, fixed to the timber framing with large, flat, plastic headed pins so as to reduce the possibility of moisture getting in through the holes made by fixings. A generous overlap was provided at joins in the paper and special attention paid to detailing around openings to insure an effective moisture proof barrier.
Board Over
The primary purpose of boarding over the timber framework is to provide a consistent solid surface to attach the external cladding to, it should also provide an additional barrier against the weather without preventing the walls from being able to breath. After we have gone to the trouble of applying building paper, it would be pointless to put an impermeable barrier outside this for internal moisture to get trapped behind. The reason we use external quality plywood is to provide durability because it is effectively outside the moisture barrier (building paper), it will be exposed to moisture vapor but will be protected from rain and snow by the external cladding. That is why the slight gaps between the boards are not sealed so as to allow moisture to escape from the inside. This is especially important in countries that get very cold in the winter because all external openings are rarely opened and effectively sealed, preventing heat loss but minimizing ventilation, this is not good for the building structure or our health.
 Narrow shafted pins or screws with large flat heads are again used to minimize moisture penetration where the fixings pierce the building paper.


        

External Cladding

The cement cladding boards were then cut and attached to the plywood boarding and underside of the roof verge overhang with a generous overlap for added weather protection. Narrow shafted, wide headed screws were employed again as fixings, it is important to pre-drill and countersink cement boards as the are brittle and unforgiving. As can be seen below, the building paper protrudes over the window frame, this will eventually be fixed behind the window surround, when fitted. The fixing heads and bare patches on the cement boards where they were cut are then painted with weather resistant paint of the same colour for corrosion resistance and aesthetics.