Loft insulation in Cardiff is one of the simplest ways to make a house warmer and cheaper to heat. Heat rises, and in a home with a thin or patchy layer of insulation a large share of it is lost straight through the ceiling and out through the roof. Bringing the loft up to the widely recommended depth of 270mm of mineral wool stops a lot of that.
We install loft insulation from scratch in lofts that have none, and top up lofts that only have the 50mm or 100mm that was common decades ago. We also strip out old, damp or contaminated insulation where it is doing more harm than good. Most standard jobs are done in a single day, and we leave the loft tidier than we found it.
What loft insulation is and who it suits
Standard loft insulation is a layer of mineral wool laid across the loft floor, between and over the ceiling joists. It keeps the heat in the rooms below and leaves the roof space itself cold and ventilated. This is called a "cold loft", and it is how most houses in Cardiff are built, from Victorian terraces in Roath and Canton to post-war semis and modern estates.
It suits you if:
- Your loft is used for little or no storage and you are not planning to convert it.
- You can see the tops of the joists, which means there is less than about 100mm of insulation.
- The existing insulation is flattened, patchy or missing in places.
- You have just bought a house and have no idea what is up there.
If you want to use the loft for storage, insulation on its own is not the full answer, because standing boxes on mineral wool squashes it. In that case we would usually pair it with raised loft boarding so you get both. If the loft is used as a room or the roof is too shallow for 270mm on the floor, SuperFOIL multifoil fitted to the rafters may suit you better.
Signs your loft needs insulating or topping up
- You can see the joists. If the tops of the timbers are visible, there is not enough insulation.
- Upstairs rooms are cold even with the heating on, or bedrooms get very hot in summer.
- Snow or frost melts quickly on your roof compared with the neighbours. That is your heat going through it.
- The insulation is grey, crumbly or compressed, or has been pushed aside by previous trades.
- There are droppings or nesting in it. Contaminated insulation should come out, not be topped up.
Not sure how deep yours should be? Our guide on how much loft insulation you need explains how to measure it and what the numbers mean.
Materials we use
We use Knauf Earthwool mineral wool loft roll. It is soft to handle, non-combustible, and does not rot or attract pests. Mineral wool works by trapping still air in its fibres, so it only performs properly when it is laid at full thickness and left uncompressed.
Cross-laying to 270mm
We lay the first layer between the joists, filling the gaps fully. The second layer goes over the top at right angles to the joists. Cross-laying covers the timbers, which would otherwise act as cold bridges, and closes the gaps between rolls so heat cannot slip through the joins.
Hatch, tanks and pipes
The loft hatch is often the weakest point. We insulate the back of it and fit a draught-proofing strip around the frame so warm air does not pour through the gap. Cold water tanks are insulated on the top and sides but not underneath, so a little warmth from the house keeps them from freezing. Exposed pipework in the loft gets lagged, because once the loft floor is properly insulated, the roof space above it gets colder.
Doing it properly: the details that matter
Keeping the eaves ventilation clear
A cold loft needs air moving through it to carry moisture away. Stuffing insulation hard into the eaves blocks that airflow and can lead to condensation and mould on the underside of the roof. We stop the wool short of the eaves or fit eaves ventilators so the gap stays open. If a loft already has damp or black mould, we fix that first: see loft mould treatment.
Downlights and cables
Older recessed downlights in the ceiling below get hot, and insulation should not be piled directly on top of them. We keep it clear or fit suitable covers. Electrical cables are lifted over the insulation where practical rather than buried under it, so they do not run warm. If we spot wiring that looks damaged or unsafe, we tell you rather than covering it up.
Removing old or contaminated insulation
Topping up only makes sense if what is already there is clean and dry. Insulation that is wet, mouldy, or soiled by mice, rats or birds gets bagged and taken away before we start. It costs a bit more, but laying new wool on top of a problem just hides it.
What affects the cost
Loft insulation starts from £600 installed. The final price depends on:
- Loft size. More floor area means more rolls and more time.
- What is already there. A top-up over clean insulation is quicker than a full install. Stripping out old or contaminated material adds labour and disposal.
- Access and clutter. A loft full of stored items needs clearing first, either by you before we arrive or by us.
- Extras. Hatch insulation, tank and pipe lagging, eaves vents and downlight covers.
Your quote lists each of these separately, so you can see where the money goes. Depending on your household circumstances you may also qualify for grant funding in Wales; it is worth checking before you pay for the work yourself.
What happens on the day
We arrive at the agreed time, put dust sheets down on the landing and under the hatch, and set up lighting in the loft. Rolls come up through the hatch already compressed in their packaging, so there is no need for large access.
If old insulation is coming out, it is bagged in the loft and carried down carefully. We then lay the new wool between the joists, cross-lay the second layer, deal with the hatch, tanks and pipes, and check the eaves are clear. Walkways or boarded areas can be added at the same time if you have asked for them.
Most standard jobs in Cardiff homes are finished in one day. Before we leave we hoover the landing and talk you through the finished loft, so you can see what you are paying for without climbing up yourself.
Aftercare and what to expect
Once the job is done there is nothing to maintain. Mineral wool keeps working for as long as it stays dry and uncompressed. A few things to keep in mind:
- Do not store things on the insulation. Squashing it reduces how well it works. If you need storage, ask about raised boarding.
- The loft will feel colder. That is a good sign: the heat is staying in the house.
- Tell other trades. Electricians and aerial fitters should put the insulation back as they found it.
- Glance up once a year. Look for damp patches, droppings or flattened areas, especially after storms.
We cover Cardiff and the surrounding towns, from the city centre out to Penarth, Barry, Caerphilly and Newport. See all the areas we cover, or call us on 0800 229 4668 to book a free survey.
