Don't Get Caught using metal web joists
As a self-builder, one of the key decisions you’ll face during your project is whether you go with a timber-frame structure or not. If you do, there are still many options to choose from.
The standard, solid timber joist construction method is one that we’re all familiar with. But, when it comes to designing the services for your building, this can also throw in a few curve-balls.
Electrical wiring is fairly simple, given the small dimensions. Plumbing works - not quite as easy but the solid joists can accommodate cut-outs big enough to allow these to run to where they need to.
Ventilation: slightly trickier. Ducting sizes are conventionally either circular 125mm diameter or 204x60mm rectangular PVC ducting. These can be difficult for the solid timber joists to accommodate whilst keeping their structural integrity. You can always put in a service void, but who wants to lose out on that all important ceiling height? So the answer is webbed joists!
Now, before you start feeling too pleased with yourselves, please remember a few things when considering your ducting routes and sizes.
Firstly, even using webbed timber joists, check that there is enough depth and width within the web to take either of the standard ducting sizes. Like ducting, webbed joists come in all shapes and sizes so be sure that yours is big enough!
Remember that if you go with a branched PVC ducting system, they will come to site in 2m lengths. So be sure to plan in the installation whilst you still have access to slide a 2m length of duct through the webbed joists, as having continuous runs of ducting ensures that the systems stays as airtight as possible.
However, if the scenario arises where you need to cut the PVC ducting into lengths that can be inserted in between your webbed joists,it is hard to ensure that you retain that all-important air tightness resulting in a poor system.
Not all is lost ! you could utilize a radial ducting system. This consists of multiple runs of 75mm semi-rigid duct from centralised manifolds, this insures airtightness and an efficient system
BPC Ventilation have a range of radial systems from Airflow and our home brand Quiet-Vent allowing for installation to almost any type of construction