17 Sep V is for… ventilation
We’re so close to the end of our A to Z guide to loft conversions now. It’s hard to believe just how fast the time has gone. Today we will be focusing on ventilation.
This is especially important for those of you planning to use your newly converted loft as a bathroom or kitchen, but it’s also applicable to all lofts. Read on for our top tips to make sure your loft is well ventilated.
Ventilation for the roof
Most roofs are classed as cold roofs, with insulation being installed along the ceiling joists. This ensures maximum ventilation in the roof space, preventing roof timber from decaying and reducing the likelihood of mould settling from condensation. By installing a loft conversion however, insulation will then be needed between the rafters, thus restricting the amount of air flow.
In order to ensure that your loft is sufficiently ventilated, you’ll need to take the roofing underlay into consideration. Your loft will either have high resistance underlay (HR) or low resistance (LR) underlay.
HR underlay with ventilated void
For this type of underlay, it is important to ensure that your ceiling is well sealed and that the vented voids between the insulation and underlay are 50mm in depth, to provide enough space for air flow. However, it may be that there are some areas where it is difficult to leave a 50mm gap. If your loft has dormers, fire barriers or changes in roof pitch, this will create separate voids in the roof slope. If this is the case, you should make sure the following steps are adhered to:
– Additional vent openings below the obstruction equivalent to 5mm x length of obstruction
– Additional vent openings above the obstruction equivalent to 25mm x length of obstruction.
LR underlay with no void
If your roof is fitted with low resistance underlay then you do not have to worry about providing voids. You should however ensure that there is a vapour control layer below the insulation. If there are joints in this, make sure that there is at least 100m lap and that it is well sealed. Often, a polyethylene sheet can be used as the vapour control layer.
In order to prevent condensation from occurring, you’ll have to make sure that the ceiling is well-sealed and that there is enough air movement between both the underlay and the roof covering for any moist air to be released back to the atmosphere.
Regulations for ventilation in lofts
– All new loft conversions must have both rapid and background ventilation – you’ll need to install a window that is at least 1/20th of the total floor space to provide this.
– For loft bathrooms, mechanical ventilation will need to be installed – it should be able to extract at least 15 litres per second.
– To prevent condensation from forming, roof voids need to be well ventilated.
– There must be at least 50mm air space between the roof and the insulation material unless you live in an older property that has no roofing felt.
So there you have it – ensuring that your loft space is well ventilated is important. It is always best to ask an expert if you are unsure about the type of underlay your roof has.
If you are planning a loft conversion for your home, take a look at our gallery for plenty of design inspiration. Our client testimonials show exactly why we’re the right firm to complete the job.
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