Insulating a Shed - Five Ways To Improve The Thermal Performance Of Your Shed

Imagine it is October in the Northern hemisphere, the evenings are getting cooler and some mornings it is getting a little bit frosty.

What is your first reaction as to the clothes you wear?

Right, it is to put on a jumper or a thicker coat. As the season progresses and the weather gets even colder you also might add a woolly bobble hat and a pair of insulated boots.

Insulating a shed is bit like adding some extra layers of clothing

Not all sheds are suitable to be insulated. If you have a small plastic or metal shed then their initial construction does not really suit the process that I am about to discuss. If you have a shed like this you would be better off changing the shed for a more robust type of shed that can more easily accept the additional insulating materials. But if you have a fairly standard type of timber shed, using a minimum of 3x2 timbers there is a fair amount that you can do to help it retain the heat better in the colder months.

So what are the main areas to think about when insulating a shed?

There are five main areas to address when 'winterising' your shed, these are;

  1. Wall insulation
  2. Roof insulation
  3. Floor insulation
  4. Upgrading doors and windows
  5. Improving air tightness

The thickness of insulation that you need to insulate a shed depends on a wide variety of factors

The main factors that influence the thickness of the insulation are;

  • The reason why you are insulating the shed (is it just for storage or is it going to be used as an office)
  • The local climate (sheds in Arizona need less insulation than Northern Canada)
  • and
  • The type of insulation material that you use

The type and thickness of insulation that you select is the topic for another article, so for the moment lets just consider the different locations that you will need to insulate. Starting with the shed walls.

1. Let's start by looking at the wall insulation

Typically timber shed walls are built with vertical timber 'studs' at 2' (600mm) centres. The studs are generally 4x2 but can be 3x2 or even less in some cases. The insulation fits between the studs and then a lining board is fixed to the internal face of the studs.

The insulating properties of different materials vary widely. For example 50mm of of phenolic foam board has the same capacity as 100 mm of mineral wool. Your choice of insulating material will vary depending on cost, availability and the size and makeup of your shed. There will be more details of the types of insulation future articles.

2. Roof insulation

Insulating a shed roof is typically done using insulation below the roof deck and between the rafters. Care is needed to ensure that there is sufficient ventilation space between the underside of the roof deck and the top of the insulation. For a heated shed warmer air inside rises and can have a relatively high moisture content. As the warm air reaches the cold roof timbers it condenses and if there is not sufficient ventilation space above the rafters the moisture accumulates and the roof timbers start to decay.

When insulating a shed roof you need to ensure that there is at least a 2" gap above the top of the insulation and that there are ventilators at the eaves. The ventilators allow air to flow in one side and out the other bringing in fresh air and exhausting the moist and damp air from above the insulation.

3. Floor insulation

Insulating a shed floor is not one of the first things that comes to mind when insulating a small building. Warm air rises and so naturally the walls and the roof are the first areas to consider. However having a layer of insulation beneath the floor boards will contribute towards keeping the contents of the shed toasty.

4. Doors and Windows

The standard doors that are supplied with sheds are fairly thin and although they are suitable for use in an unheated building they may not be suitable for stopping the heat escaping. Also there may be no draught stops around the door so this will be a way that heat can escape.

For windows the frames may not be thermally broken, if they are metal and almost certainly the windows will be not be double glazed.

For the windows double glazed windows retain a lot more heat than single glazed ones. Also the frames need to be considered too. Timber frames will most likely be OK however metal frames should be of a thermally broken design to avoid it running with condensation in the cold weather.

The problem that will occur with substandard windows and doors is condensation. The warm air inside the shed will have a greater capacity to carry moisture than the colder exterior. When this warm air comes into contact with a single glazed window pane or what is known as a 'cold bridge' the moisture in the air condenses on to the surface. Having correctly specified double glazed and thermally broken windows should eliminate this problem of condensation.

5. Improving the air tightness of the building

Insulating a shed is not just a matter of adding insulation. Reducing heat losses through upgrading the doors and windows will be a big step towards reducing draughts in the building. Other areas where you might be able to reduce draughts are at panel joints, the junction between the roof and walls and anywhere there are penetrations through the building envelope such as for electricity supply etc.

In contrast to your cold weather gear, insulation helps in the summer too

Unlike your winter togs, you don't need to remove the insulation that you install on your shed as the weather gets warmer in the Spring and Summer. The insulation that you have added has the great benefit of also keeping the heat out and the shed a little cooler in the summer.

So as you adjust to your summer-wear of shorts and T-shirt your shed can stay in its salopettes and ski jacket right the way through July and August!

Next step

This article discusses a practical example of retro-fitting insulation to a garden office

This article looks a bit deeper at the properties of the different types of insulation

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