How to Insulate your Loft Without Losing your Loft Storage Space

One of the most commonly faced difficulties is how to add insulating material to a loft space when the floor has already been boarded and the loft is used for storage.

When you are standing in the loft, the depth of the void formed between the plasterboard of the ceiling below and the top of the ceiling joists is usually about 100mm (4”). Given that current building regulations in the UK require 270mm of insulating glass wool, if a home owner wishes to retain a boarded loft and does not want to use a “spray-on” insulation product up between the roof rafters then there is a choice to be made about which direction to take. The main choices are between:

1. Building the joists up with additional “packing joists” to create a 270mm void which can then be filled with insulating material and then re-boarded over.

2. Using a solid insulating board cut to fit in the void that exists between the joists without raising the level of the loft floor.

3. Insulating between the roof rafters with either insulating board, spray on insulation products or insulation blanket products.

This article focuses on the first two potential methods, and looks at their pros and cons.

Before reading the article, please note that there are a number of dangers associated with carrying out work in your loft and great care must be exercised. Follow all safety instructions available from the suppliers of the materials you decide to use and if you have any doubts about your capability to carry out insulation work in your loft safely please consult a qualified builder or insulation contractor.

- Building the floor level up: Pros

1. If you run the additional “packing joists” across the existing joists at 90 degrees, you are able to run wool insulation over the top of the original ceiling joists) which reduces potential “thermal bridging”.

2. The materials are, in total, probably less expensive that using insulating board

3. You retain most of your loft storage area.

- Building the floor level up: Cons

1. It’s a big DIY challenge

2. The wood required for the “packing joists” may be heavy and difficult to manoeuvre into position

3. You lose some height in the loft because of the floor being raised

- Insulating with insulation board between the existing joists: Pros

5. Your floor stays the same height and therefore no loft height is lost.

6. You retain your loft storage space

7. There are no heavy timbers to work with

- Insulating with insulation board between the existing joists: Cons

1. Its time consuming and fiddly to cut insulation board to fit between existing joists (which are invariably, even within one loft, are different widths apart). The cutting to size of the thermal boards usually needs to be done before they are taken into the loft space as access is usually restricted but it is also important that any dust resulting from the cutting does not contaminate the property’s living space

2. Insulation board can be costly (up to £50 -£60 a sheet depending on the gauge) and care is needed to cut them safely as the resulting dust acts as an irritant

3. Because you are insulating between the ceiling joists you are (by definition) not insulating over the ceiling joists. This means that where the joists run, your insulation is limited to the thermal properties of the joist timber only and your insulation will be “bridged” by the timber i.e. cold will be able to be transferred through the timber joists.

4. Where a home has been built with traditional 4” x 2” timber ceiling joists you are unlikely to get much more than 90mm of insulation board in between the joists (this will vary from property to property). It might be that if there is any old fashioned electrical conduit that needs to be worked around, you get even less than 90mm in.

Issues to worry about include thermal “bridging” when building up the joists to get the required height or when filling between the joists and re-boarding straight over the original joists.

From a pure insulation, building regulations and “required effort” point of view the best solution is getting a professional contractor in to carry out the required work.

To sum up, if retaining storage space in your loft is important then you can improve your level of insulation but you may have to compromise on the level of insulation you ultimately have and you have to be realistic about the difficulty and complexity of the DIY task involved.