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Underfloor insulation can dramatically improve comfort

Posted by greentomatoenergy . on 2 April 2013 at 10:04 am

Now that we’re (almost) through winter, we have had a number of calls from clients who felt the cold through their wooden floors and have asked us about insulating them. â€¨The first thing to say is that underfloor insulation can make a dramatic difference to comfort levels, particularly if you have bare suspended timber floors.

The second thing is that draughts significantly affect the performance of the insulation. This means that even if you install lots of insulation, if there are gaps which allow the cold air through, it won’t improve your comfort levels as much you might have hoped. It’s therefore better to close the draughts and ensure that the work is as airtight as possible. Our preferred method is to install celotex boards, cut to size to fit in between the joists, and to then tape up the junctions between the boards, the timbers and the walls.

This obviously requires all the floor boards and skirting boards to be removed. Whilst there are a number of other methods that do not require this level of disruption, they generally require the existence of a large crawl space underneath the floor. However, even if a crawl space exists, it can be very difficult to achieve satisfactory levels of air-tightness. There are shortcuts, but nothing beats taking up the floors and ensuring that it’s done properly.  

This means that the work is likely to be disruptive and expensive, particularly if the flooring is tongue and groove flooring because this needs to be taken up very carefully and replaced in exactly the same way as it was installed. Very often it might be impossible to take all the boards up undamaged. Sometimes these can be replaced with reclaimed boards, or you might think of it as a good opportunity to replace all your boards.

The latter option increases the material cost but can reduce the cost of installation as less care is needed when taking the boards up. This means that it’s unlikely to meet the golden rule for green deal purposes, but if your ground floor is cold and uncomfortable, this work will make the floor just as comfortable as your upper floors!

If you do decide to insulate under your suspended floor, one crucial issue to consider is ventilation. If the void under the floor is not sufficiently ventilated, installing an airtight layer between the floor and the ground will trap moisture and lead to damp and the potential decay of the timbers. 

Find out more about insulation on YouGen

Introduction to insulation

A case study of DIY underfloor insulation

An introduction to cavity wall insulation

An introduction to solid wall insulation

by Inigo Harrison

Photo Credit: pareeerica via Compfight cc

About the author: greentomatoenergy specialises in cost-effective renewable technologies and low carbon building.

If you have a question about anything in the above blog, please ask it in the comments section below.

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1 comments - read them below or add one


Anthony525Comment left on: 29 April 2013 at 8:32 pm

There is some misunderstanding concerning under floor insulation.

If the timber used to make a floor, joists and floor boards, is kept warm and above the dew point in the crawl space then there is no chance of the timber absorbing water vapour.

This is achieved quite easily, by simply boxing in the joists, once the joists are enclosed the heat from the room above keeps the joists warm.

You can also stop warm wet air from entering the crawl space by blocking the air vents. About two hundred times a year we have frost or dew on the ground this is due to the water vapour in warm wet air condensing on the cold ground. At the same time the stack effect inside the home pulls the warm wet air into the crawl space where the water vapour in the air is absorbed into the below dew point joists. (The description warm wet air related to the outside air temperture which is above the dew point of the cold surface)

Blocking the air vents and sealing the floor not only keeps the floor warmer it reduces your heating bills by stopping outside cold air (air that is colder than the conditioned air in your comfort zone) from entering your comfort zone.

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