Laying insulation across the open middle of a loft is straightforward. The time, and the risk, is in the details: the recessed lights poking up through the ceiling, the cables snaking across the joists, the water tank, the pipes, the boiler flue and the bathroom extractor duct.
Each of these needs handling differently, and getting them wrong can mean anything from a frozen pipe to a fire risk. This guide goes through them one by one.
Recessed Downlights
Recessed downlights sit in holes cut through the ceiling, with the body of the fitting in the loft. They produce heat, and many are not designed to be buried in insulation. Covering an unsuitable fitting can make it overheat, shorten its life, and in the worst case create a fire risk, particularly with older halogen lamps that run very hot.
| Type of fitting | Can insulation go over it? | What to do |
|---|---|---|
| Fitting rated as suitable for covering with insulation | Yes, as the manufacturer allows | Lay insulation over it in line with the instructions |
| Fitting with a suitable fire-rated cover or hood fitted over it in the loft | Yes, over the cover | Make sure the cover suits the fitting and is seated properly |
| Fitting with no rating or cover, especially old halogen | No | Keep the clearance the manufacturer specifies, or have covers or new fittings installed |
| Separate transformer or LED driver | Do not bury it | Lift it to sit on top of the insulation where it can stay cool and accessible |
Downlights are also holes in the ceiling. Warm, moist air rises through them into the loft, which wastes heat and adds to condensation. Covers that seal over the fitting help with both problems.
Electrical Cables
Electrical cables get warm when they carry current. In open air that heat escapes easily. Wrapped in insulation, it cannot, so the cable runs hotter. The UK wiring regulations deal with this by reducing the current a cable is allowed to carry when it is surrounded by insulation.
Most lighting circuits carry so little current that this rarely matters. It matters more for heavily loaded circuits, such as electric showers, cookers, immersion heaters and some heating systems, if their cables run through the loft. Burying those under 270mm of insulation can push them past what they were sized for.
- Lift cables onto the insulation wherever there is slack to do so, rather than burying them.
- Do not pull or strain cables to make them reach; if they will not lift, leave them and mention it to an electrician.
- Keep junction boxes accessible and visible on top of the insulation.
- Ask an electrician about any thick cables, which usually belong to high-current circuits.
The Cold Water Tank
The cold water tank is the one place where you want less insulation, not more. In winter, a little warmth rising from the house through the ceiling directly underneath the tank helps stop it freezing. Insulate under it and you cut that warmth off, leaving the tank sitting in a cold loft.
Leave the ceiling under the tank uninsulated. Run the loft insulation up to the edges of the tank area, then insulate the sides and top of the tank itself with a jacket or boards, so the insulation goes over the tank rather than under it. Make sure the tank has a fitted lid.
Water Pipes
Water pipes in a cold loft are the most likely thing in the house to freeze. Once the ceiling is properly insulated, the loft gets colder, which makes this more likely, not less.
- Lag every pipe in the loft with foam pipe insulation, including the overflow and the pipes to and from the tank.
- Pipes running between the joists can sit under the loft insulation, on the warm side, where they are protected.
- Pipes running above the insulation need lagging all the way along, with joints and bends covered.
Flues and Chimneys
Some boiler and fire flues pass through the loft, and chimney breasts often run up through it. Flues can get hot, and combustible materials must be kept away from them by the clearance set out in the appliance or flue manufacturer's instructions. Do not pack insulation around a flue pipe. If you are not sure whether a pipe in your loft is a flue, or whether it is in good condition, have it checked before insulating around it. In older homes, old cement flue pipes may also contain asbestos and should not be disturbed.
Extractor Fan Ducts
Bathroom and kitchen extractor fans often run a flexible duct across the loft to a vent in the roof or wall. Warm, wet air travelling through a cold, uninsulated duct condenses inside it, and the water can run back down into the fan or drip onto the ceiling.
- Make sure the duct goes outside, not just into the loft space.
- Use insulated ducting or wrap the existing duct.
- Keep it as short and straight as possible, sloping slightly away from the fan where you can.
The Loft Hatch
The hatch is the biggest single gap in most insulated ceilings. Fix insulation to the back of the hatch door and fit draught strip around the frame so it closes onto a seal. It stops heat escaping and keeps moist air out of the loft.
A Quick Checklist Before You Insulate
| Item | Check |
|---|---|
| Downlights | Rated for covering, or fitted with covers, or given clearance |
| Cables | Lifted on top where possible; thick cables flagged to an electrician |
| Junction boxes and drivers | On top of the insulation and accessible |
| Water tank | No insulation underneath; sides and lid insulated |
| Pipes | All lagged, including the overflow |
| Flues | Clearance kept; condition checked |
| Extractor ducts | Vent outside; insulated |
| Eaves | Insulation to the wall, airflow kept open |
| Hatch | Insulated and draught-stripped |
For the depth of insulation to aim for, see how thick should loft insulation be. If the existing insulation needs clearing before any of this can be done properly, our loft insulation removal service takes it back to the joists so everything above can be checked and set out correctly.
Frequently Asked Questions
Can you put loft insulation over downlights?
Only if the light fitting is designed to be covered by insulation, or it is fitted with a suitable fire-rated cover or hood that gives it the clearance it needs. Otherwise keep insulation back by the distance the manufacturer specifies. If you are unsure what fittings you have, ask an electrician.
Is it safe to cover electrical cables with loft insulation?
Cables can be covered, but they run warmer when surrounded by insulation because the heat cannot escape. Under the wiring regulations a cable totally surrounded by insulation for more than half a metre may only carry about half its normal current. Lift cables to sit on top of the insulation where possible, and ask an electrician about heavily loaded circuits such as showers and cookers.
Should I insulate under my loft water tank?
No. Leave the ceiling directly under the cold water tank uninsulated so a little warmth from the house rises to it. Insulate the sides and lid of the tank and lag the pipes instead. Carrying the insulation over the tank, rather than under it, keeps it from freezing.
Do LED downlights get hot enough to matter?
LED lamps run much cooler than old halogen ones, but the fitting and its driver still produce some heat and many are not designed to be buried. Check the fitting's rating and the manufacturer's instructions rather than assuming.
How close can insulation be to a flue?
Keep combustible insulation away from flue pipes, chimneys and anything that gets hot, using the clearance in the appliance or flue manufacturer's instructions. If a flue passes through the loft, have it checked before insulating around it.
Related Reading
Need a Hand With Your Loft?
Having your loft insulated or cleared? Send a couple of photos from the hatch, including any lights and the tank, and we will give you a written price.
Or email info@loftrestore.co.uk. Based in Cheshire, working across the UK.