Quick answer: You can board over loft insulation, but the boards should sit on raised legs or stilts so there is a gap above the insulation. Laying boards straight onto the joists over 270mm of mineral wool crushes it, and crushed insulation doesn't work properly. Raised loft boarding keeps the full depth of insulation underneath, leaves an air gap and gives you a usable storage deck.
Lots of people want a warm house and somewhere to put the suitcases and Christmas decorations. You can have both. This guide explains the problem with the old way of boarding and how to do it properly.
Why you shouldn't board straight onto the joists
The recommended depth for mineral wool loft insulation is 270mm. Ceiling joists in most houses are much shallower than that, so if you nail boards straight onto them you have two bad options:
- Squash the insulation down to the depth of the joists. Mineral wool insulates by trapping still air, so compressing it greatly reduces how well it works.
- Leave the top layer out under the boarded area. Then that part of the ceiling has only a thin layer, and often the joists are left uncovered too.
Either way, the boarded area becomes a weak spot. Boards sitting directly on the wool can also trap moisture, because there is no space for air to move above the insulation. Our guide to loft condensation and ventilation explains why that matters.
How raised loft boarding works
Raised boarding uses legs, sometimes called stilts or joist extenders, fixed to the tops of the joists. The boards are then fixed to the top of the legs, high enough to clear the insulation. The result is:
- the full depth of insulation underneath, laid between and across the joists as normal;
- an air gap between the top of the insulation and the underside of the boards;
- a firm deck for storage that doesn't press on the wool.
Our raised loft boarding uses legs that lift the boards above 270mm of insulation, so you don't have to choose between storage and warmth.
Things to check before boarding
Get the insulation right first
Once boards are down, the insulation underneath is hard to get at. So it makes sense to check its depth and condition first and top it up or replace it if needed. See how thick loft insulation should be for how to measure it, and our loft insulation page for how we install it.
Headroom
Raising the boards above the insulation lifts the floor level of the storage area. In lofts with a low pitch, that can leave limited headroom. We look at this on the assessment and plan the boarded area where it is most usable.
Weight
Ceiling joists in many homes were designed to hold up a ceiling, not to carry a heavy load. Loft boarding is for light to moderate storage, such as boxes, bags and seasonal items. It isn't a substitute for a loft conversion, and heavy items should be avoided. If you plan to store anything unusually heavy, tell us at the assessment.
Services and access
Cables, pipes, junction boxes and the water tank need to stay accessible. Boarding is planned around them, and we keep a clear route to the tank and any fittings that may need attention later.
Ventilation
Boarding shouldn't reach so far into the eaves that it blocks airflow. We usually board the central part of the loft, where the headroom is, and leave the edges clear.
How much of the loft should you board?
Only what you need. Boarding the central walkway and a storage area near the hatch is usually enough for most households. Boarding right into the eaves gives little usable space and makes ventilation and access harder. We will suggest a layout on the assessment and the written quotation will state the area to be boarded.
Getting into the loft safely
A boarded loft gets used more, so safe access matters. If you are still balancing on a stepladder to reach the hatch, a fitted loft ladder makes life much easier. At the moment we offer a free metal loft ladder fitted with any loft boarding package over 15m², subject to survey.
What about existing boards?
Many lofts already have a few boards nailed straight onto the joists, often over a thin or crushed layer of insulation. These can usually be lifted, the insulation underneath topped up or replaced, and the area re-boarded on raised legs. If the old boards are in good condition they can sometimes be reused. We check this on the assessment and the quotation says what will happen to them.
Can I board the loft myself?
Raised boarding kits are available, and a confident DIYer can fit them. The things that most often go wrong are crushing the insulation while fitting the legs, blocking the eaves, overloading the joists and boarding over cables. If you would rather have it done for you, the work is carried out by The Insulation Company or an approved installation partner, and it is often combined with a top-up so the insulation is laid first and the boarding goes on top.
We fit raised boarding in homes across Teesside and the North East. For a sense of how a combined job runs, see how long loft insulation takes.
Every job starts with a free assessment and a written quotation that sets out the scope, materials and price before anything is agreed. The work is carried out by The Insulation Company or an approved installation partner. Call 0800 229 4668 (Monday to Saturday, 8am to 6pm) or request your free assessment online.