Why timber frame isn't always quicker
One of the biggest questions every would-be selfbuilder has to address is whether to go brick and block or timber frame. For me, it’s something of a hoary old chestnut, having built using both methods and having been writing articles around this issue for many years. You’d think I’d have pretty set views by now but I don’t. Partly this reflects my tendency towards hopeless prevarication in all things, but it’s also undoubtedly because it’s a question with no easy answers.
However, a site visit this week to a timber frame house in Cambridgeshire gave me pause to think afresh about the issue. This was a site in a conservation area and that meant that there were some quite prescriptive design guidelines: basically it had to match up to the house next door, which was a detached vaguely-Georgian style brick house under a slate roof.
However the new house design was L-shaped, a stepped L-shape no less. What I mean by that is that it consisted of a main rectangular-shaped box (or aisle) of two storeys, with a single storey rear extension. My attempt at the relevant 3D house design is pictured here (blogger.com permitting). A common enough house layout, you’d think. And you’d be right.
The junction of the two parts of the house is what I wish to draw your attention to. It’s referred to as an abutment. However you do it, it causes problems because there are waterproofing details to be made between the wall of the main aisle and the roof of the extension. Lead flashings have to be fitted over the junction and the wall cavity has to have an effective barrier laid across it in order to drain any cavity water out onto the extension roof. If not, you risk the cavity draining directly down into the house below the junction. Messy.
The subject of cavity barriers can wait for another article. What I am driving at here is the disruptive effect this all has on the construction of a brick-clad timber framed house. On a simple rectangular-shaped house, or even a more complex one, as long as it has a single eaves level all the way around, the brick cladding is taken off the critical path and can be completed at leisure after the framers have departed. Indeed it can go on simultaneously with the roof covering and the fit out inside.
However, split the roof levels like this and the brick wall of the main aisle has to be completed before the extension roof can be covered over. Indeed, on the site I was on, space had to be left for the brickies to have access to the wall, which was being built-up off a steel beam over the opening. Not even the extension roof carpentry could be completed.
Result? Weeks had been lost waiting on the brickies. The roofers had been in and finished the main aisle but had to return for another visit to cover the extension. The scaffolding was gently racking up hire charges. The house could not be effectively waterproofed, let alone secured. All the supposed speed of construction advantages, which timber frame sells itself on, had been lost. In fact it would probably have been quicker to use brick and block on this house.
Had it been such, you would not have noticed that there was a problem here because the roof carpentry wouldn’t have started on either roof until the brickies had got to eaves level all around. And had the external skin been anything other than brick (or stone), the wall above the extension roof could have been finished off at leisure off some form of adapted scaffolding. Boarding, render on mesh, hung tiles, all fine: they are hung off the timber frame and wouldn’t disrupt the critical path. But bricks? They have to sit on something, be it a steel or a foundation: they can’t be ‘hung’ off the background timber frame and they can’t be built-up off the roof cover. So bricks have to be in place before the extension roof cover can be laid.
There’s a lesson in here somewhere. To simplify it right down to basics, despite what the salespeople say, bricks really do work best with blocks behind them. And timber frame is really seen at its best when it’s clad in something other than brick or stone.
Labels: Timber Frame/MMC