My Loft Is Already Boarded: Can It Still Be Insulated Properly?

Why this comes up so often

When homeowners book a survey with us, one of the most common answers to "what insulation is in your loft?" is simply "it's boarded over". Someone, often a previous owner, has laid chipboard or floorboards straight across the joists to make the loft usable for storage. Underneath, there is usually a layer of old insulation that nobody has looked at for years.

The boards themselves are not the problem. What matters is what they are sitting on, and how much space is left for insulation between the ceiling below and the underside of the boards.

What is usually under the boards

Ceiling joists in most houses are well under the depth of insulation recommended today. For mineral wool, 270mm is the widely used benchmark. If boards are fixed directly onto the joists, the insulation underneath can only ever be as deep as the joists, and anything that was deeper has been pressed down to fit.

Squashed insulation holds much less still air, so it does far less than its original thickness suggests. It is also common to find gaps where insulation was never laid, sections pulled back for cables, and dust and debris that have built up over the years. None of this can be seen until the boards come up.

Option 1: lift the boards and insulate underneath

The simplest fix is to lift the existing boards, deal with what is underneath, and insulate the loft floor properly. If the old insulation is in reasonable condition it can sometimes be kept and built on. If it is compressed, damaged, damp or dirty, it is usually better to remove it and start again. Our article on when old loft insulation should be removed explains how that decision is made.

This option makes sense if you no longer need the boarded area for storage, or only need a small part of it.

Option 2: replace with raised boarding

If you want to keep using the loft for storage, the boards can be replaced with raised loft boarding. Raised boarding sits on supports fixed to the joists, so the new boards are lifted clear of a full-depth layer of insulation instead of crushing it. You keep your storage space and the insulation underneath can do its job.

Raised boarding is for boxes and luggage, not for turning the loft into a room. It is usually kept to the central area of the loft near the hatch, where it is easiest to reach, with the rest of the loft floor insulated to full depth.

Things we check before recommending either option

• Damp and ventilation. Boarded lofts often have little airflow at the eaves. We check moisture levels in the timbers and how the roof is ventilated, because adding insulation without enough ventilation can lead to condensation. See loft insulation and condensation.
• Cables and downlights. Wiring is often run under or across old boards, and downlights in the ceiling below need the right clearances.
• Pipes and tanks. Cold-water pipes and tanks in the loft need protecting from frost once the loft floor is better insulated.
• Access. The size of the hatch and how easy the loft is to get into affects how the work is done.

What to do next

You cannot tell how well a boarded loft is insulated by looking at the boards. A survey lifts a section, measures what is there and checks the condition of the insulation and timbers. You then get a written quotation that sets out which option suits your loft before anything is agreed. You can read more about what happens during a loft survey.