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Q&As
Will a dormer window give me enough additional head height?
I’m looking to renovate and convert the loft of my end-of-terrace Victorian house in South London, which has a hipped roof. I’d like to increase head height inside the roof space for an at home office, but not sure what the best way is to do so. Will I have enough space if I extend with a dormer window, or do I need to consider more invasive types of roof extension?
One Answer
There are a number of factors to consider, but the first is the measurements of the existing space and how to get to the space allowing sufficient clearance for a new staircase. You will also need to think of Fire Safety and show how appropriate protected routes are maintained throughout the house for emergency escape. If the overall head height is already too low, then you may not be able to create a habitable space that complies with Building Regulations. I’d suggest that you need to start with at least 2.2m clearance from the top of the ceiling joists to the underside of the ridge before thinking of to creating a useable and compliant space. What is likely to happen on the conversion is that the floor level will come up (as additional structure is needed) and the roof (ceiling) level will come down to accommodate insulation.
If you can achieve this then you have the beginning of a roof conversion project. To then create more space, adding a dormer window to the rear and potentially side of the house could be a solution. If the house is not Listed or in a Conservation Area, you could also consider taking the end hip to a gable wall. This, together with a rear dormer, will give you the most amount of space available from a roof conversion. Be careful to check the amount of additional volume you are adding as, if you want to carry this out under Permitted Development, you are limited to 40m3. If you want more space, you will need to apply for planning permission.
If these parameters are not viable, a more extreme option could be to lower the current first floor ceiling to give the heights I mentioned earlier. However, this will involve structural and refurbishment work to your entire first floor as well as the cost of carrying out the roof conversion. As your house is linked to the rest of the terrace, it is unlikely that a planning authority will let you increase the height of your ridge alone, hence having to work with the upper limit of what you already have.