The 4 loft insulation mistakes to avoid
While adding loft insulation is certainly one way to improve your home’s energy efficiency, making loft insulation mistakes can result in your hard work backfiring and leading to more problems than you even started with.
However, follow the correct advice on how to insulate a loft and there’s no doubt you and your home will reap the rewards.
With building and roofing experts to hand, we’re here to explain the most common loft insulation mistakes homeowners make so you can avoid a future that sees you ripping out your hard work and starting over again.
Mistake one: lack of ventilation
If you weren’t aware there is such a thing as too much insulation, you may be heading towards making one of the most common loft insulation mistakes – over filling your loft with insulation that can lead to a lack of essential ventilation.
“It’s very common for homeowners to insulate their lofts right up the edges or eaves of a roof, as the common perception is that if they don’t, cold air will enter into the loft space and this needs to be avoided at all costs,” says Mike Storey, roofing expert at UK Flat Roofing & Insulation.
“However, this isn’t entirely true, says Mike. “Loft ventilation gaps are essential as they allow allow any moisture build-up to dissipate. The most common insulation material used in a loft is loft roll, and as soon as this get damp or wet its thermal value is ruined, meaning its performance is reduced significantly,” he warns.
“If you block eaves vents or air bricks in lofts then this will only lead to problems,” confirms building expert, Mark Stevenson. “Your once dry loft will soon become a haven for damp and mould.”
The solution? “Make sure you have ventilation paths when insulating your loft,” advises Mark. “This means using cross flow vent trays that are fitted between the rafters at the eaves, letting air continue to flow throughout the space.”
Mike Storey is an insulation expert at UK Flat Roofing and Insulation. The company which provides a variety of flat roofing, insulation and construction supplies across the UK. It was founded in 2014 and is now one of the largest roofing and insulation specialists in the country.
Mark Stevenson
Mark Stevenson has worked as a construction professional for over 30 years and has an extensive career in housebuilding. He is currently chief operating officer for Custom Build Homes and chair of the National Custom and Self Build Association. He regularly shares his knowledge at Homebuilding & Renovating Shows and and coaches self builders about how to build their own homes. Aside from Mark’s professional career, his skills also extend to practical building knowledge as a skilled joiner, hands-on renovator and serial self-builder of his own development projects.
Mistake two: Poor installation
If, as part of your loft improvement measures you’re considering boarding your loft in order to create loft storage space, this next mistake is one you need to bear in mind.
Although maximising on storage space may be the goal, this doesn’t mean you can cram your loft insulation below the boards and hope for the best.
“A common loft insulation mistake we see us homeowners putting the loft roll into the joist space and then boarding directly over it,” confirms Mike Storey.
“This will squash or compress the insulation, and as loft roll uses the air trapped between the glass fibre strands to work, compressing it to a thickness less than it’s designed to be, stops it from working correctly,” warns Mike.
The required amount for loft insulation in accordance with Part L of the building regulations will depend on whether you are building a new self build or refurbishing an existing property.
However, when renovating a house, you’ll likely find that the maths doesn’t quite work out – making this particular loft insulation mistake an easy one to make.
“Standard joists are commonly only 150mm – 200mm deep in most roofs, meaning the insulation is automatically higher,” explains Mike. “Your best solution is always to use a product such as Loft Legs to increase the space before adding boards on top of the legs.
“Always add 50mm of ventilation gap above the insulation and below the timber floor that is connected to the eaves on both sides,” advises Mike, “or you will end up with damp issues caused by loft condensation.”
Loft Leg
Loft Legs 175mm 12 Pack
Using Loft Legs when insulating your loft and boarding it out for storage will give you the scope to lift your boards above the insulation, leaving the insulation free to work as intended
Mistake three: Gaps in the wrong places
Although the argument for leaving gaps to allow for airflow still stands when installing loft insulation, it’s not always the case when using the warm roof method for insulating your loft. This is when the roof is insulated – most commonly with insulation boards – rather than insulating at floor level between the joists.
“Even the tiniest of gaps can lead to problems in this instance,” confirms Mark Stevenson. “Gaps can result in cold spots, loss of heat and potentially issues again with mould and condensation.”
“The correct way to insulate at this level is to ensure you have ventilation above and below, and a breather membrane installed,” advises Mike Storey. “Then, always ensure the boards are taped up along the joints and at the edges. Also make sure that any damage to the foil on the board is taped, as otherwise this will compromise your vapour barrier layer.
“If it’s a multifoil system ensure that they are taped up between each roll and around the edges,” he adds. “This prevents moisture getting into the roof. You will still need ventilation at the eaves, above the insulation in order to prevent any moisture build up, but making sure it’s neatly fitted is essential.”
Shop for loft insulation products
Diall
Insulation Roll 6m X 370mm
An alternative to traditional glass wool insulation making it comfortable to work with. Easy to lay in handy sized rolls and easy to tear
YBS
Ybs Breatherquilt 10m X 1.2m
A dual purpose membrane and insulation roll, lightweight and flexible making it easy to install with no harmful fibres or particles
Rockwool
Rockwool Thermal Insulation Roll – 100/200mm
The Rockwool Thermal Insulation Roll is designed for home comfort and helps towards saving energy, especially for application in lofts
Mistake four: Using the wrong insulation or method
Choosing the right type of insulation, and how and where to install it is the best way to avoid making loft insulation mistakes in general, but how do you know?
If you’re embarking on a loft conversion, you’ll need to consider insulating at roof and floor level to make the space habitable. But what if it’s just for storage?
“Start by checking if the items in the loft need to be stored at room temperature, or if they can fluctuate between being hot in summer and cold in winter,” suggests Mike Storey. Fully insulating the space will give you maximum insulation, but this may not be necessary.
Using the right product is also key, warns Mark Stevenson. “Too often people rush to insulate without understanding that there isn’t a one-size-fits-all approach. Spray foam insulation used in between roof rafters is a prime example. This can lead to rotting timbers and expensive repairs.
“If you aren’t sure what product is best for your loft, make sure you consult with an expert first in order to pick the best solution,” he advises.
If after reading this you think it might be time for an upgrade, make sure you follow our guide to removing loft insulation safely, and work out your budget with our guide to loft replacement costs.
And finally, if you’ve suddenly realised there’s an unwanted gap in the form of a ‘bare’ loft hatch, take the time to insulate your loft hatch too.