To insulate under floorboards, choose between accessing your crawl space from below or lifting the boards from above. The most common DIY approach involves installing rolls of mineral wool between your floor joists. It is vital to maintain subfloor ventilation and protect the insulation from dampness.
By adding floor insulation boards, you create a thermal insulation barrier that keeps warmth in during the winter and out during the summer. The key benefits include: Increased Comfort: Eliminates cold draughts coming up through the floorboards, making rooms feel warmer underfoot.
To insulate suspended timber floors, insulating materials like mineral wool or rigid foam boards are installed between the floor joists beneath the floorboards.
The good news is that you can often insulate the underside of floorboards without tearing them up. Another benefit of floor insulation is that it can help a building comply with Building Regulations Part L, which sets the standard for energy efficiency.
From underneath, you can add mineral wool insulation which can be secured in place with netting. Another option is to fit rigid insulation boards. These can be cut precisely to fit snugly between the joists.
9 Best Insulation Materials for Under Floors (Above Grade)
The best products for draft prevention
Foam insulation is a common target because it's easy for them to chew through. The material offers little resistance, allowing mice to create tunnels or nests within the insulation. But mice aren't just interested in chewing for the sake of it—they're also drawn to the warmth and shelter insulation provides.
Installing suspended floor insulation can take anywhere between a few hours to 2-3 days, depending on the size of the floor area being insulated and the materials used. Simply installing spray foam may take just 2-4 hours, but taking up the floorboards and installing other materials may take much longer.
Because spray foam can trap moisture, hide the condition of the roof, make it difficult for surveyors to inspect, which means risks like timber decay, dry rot, and not forgetting increased fire risk. If you've got it or you're buying a property that does, this is something you need to know upfront.
Some underfloor areas are easier to insulate than others. Easy access to the underfloor area makes for a great DIY home project.
What time of year is Insulation cheapest?
The cost to insulate a floor varies depending on house size, the materials used and how accessible the space is under the floorboards. In 2024, Checkatrade estimated the typical cost of suspended timber floor insulation to be around £105 per square metre. Solid floor insulation costs around £70-£80 per square metre.
Under floor insulation
10 - 20% of heat lost from homes can be through floors that aren't properly insulated, according to the UK GovernmentOpen in new window.
Therefore, the Energy Saving Trust advises that insulation should not be installed where it is likely to block existing ventilation points, such as eaves or soffit vents, as this can lead to loft condensation and damp issues.
Closed cell spray foam is rigid once set. It is a better thermal insulator and was previously sold to stabilise failing roofs. But if it has been used inappropriately or installed poorly, it might put stress on timbers, restrict air circulation and put them at risk of decaying.
When balancing upfront cost and overall thermal efficiency, the cheapest and most effective standard insulation is fiberglass batt insulation. However, if you are looking for long-term savings through superior air sealing, dense-pack cellulose often provides the best overall value.
Potential problems with spray foam insulation
reduce air circulation and ventilation within a roof space. lead to dampness and condensation on the underside of a roof because it forms an air barrier and stops moisture from escaping. place timber-framed roofs at risk of decay.
Mice are curious and always searching for safe, snug, and warm nesting sites. Attics filled with blown-in insulation provide an excellent option–from the mice's point of view. As long as there is a ready food source. Mice are omnivorous and will eat and chew on almost anything including wood and electrical wires.
6 Signs Your Home Needs Subfloor Insulation
Adding more insulation does not always make a house warmer because insulation only slows heat transfer. Homes with major air leaks, moisture problems, unsealed rim joists, or empty wall cavities can still feel cold even with attic insulation rated at R-38 or R-49.
The Amish control mice through non-chemical, self-sustaining methods, relying on active trapping, natural scent repellents, and structural exclusion. Rather than using commercial poisons, they focus on physical barriers and natural predators to keep rodent populations in check.
Rats are a primary food source for a wide variety of animals. Their most significant natural and artificial predators include:
There is no single "chew-proof" insulation that will unilaterally stop a highly motivated rodent, but combining borate-treated dense-pack cellulose or mineral wool with physical exclusion materials creates an impassable barrier. Traditional fiberglass is highly susceptible to nesting.