Ventilating a shed

by Mark

Hi John

I have a gambrel style 12’x16’ shed. The old siding has seen better days, so I’ve decided to replace the worn-out siding with a new board and batten siding. I’m also going to insulate and finish the inside with plywood, install a dog kennel, add some new base cabinets, work bench and add electrical.

My major concern is ventilation.

I have no idea what I need here, if any. My future plans will be to add an electrical heater, so the dog and I can be comfortable all winter. We’re not going to condition the shed; we just need to have good ventilation all year round, so it’s not too hot in the summer or to cold in the winter.

I’m thinking of adding one Whirlybird vent on the roof through the attic into the main space.

Don’t know if this idea is good or bad.

Any suggestions?




Hi Mark,

Thank you for your question.

Before I go into my opinions on this I should perhaps back up a bit and look at the reasons why anyone might want to ventilate their shed and the options that are available.

Why would I want to ventilate my shed?

The two reasons for ventilating a shed are to disperse excess heat in the summer and also top prevent the moist, damp, stale air in the winter months.

The main reason that a shed heats up in the summer is due to the sun shining directly onto the roof. Because the roof is pointing most directly at the sun it absorbs significantly more energy than the walls. This build up of heat can make it uncomfortably hot in the shed for humans or animals and in the extreme can warp timber or melt plastic components.

In the winter dampness is more of a problem. Stale damp uncirculated air allows fungal spores to grow causing potential problems with mildew and rotting of timbers exposed to long term condensation.

Dampness from the natural moisture content in the air is one element that can be magnified when humans or animals are occupying the shed. Due to the moisture added to the air from their breath and activity.

What are the main ways to ventilate a shed?

A shed can be ventilated by adding specifically designed ventilators to the following locations: Roof, eaves, gable and also not forgetting the contribution to be made through simply opening a door or window.

Roof ventilation can take the form of a continuous vent that runs the whole length of the ridge of the shed. Other forms of ventilation near the ridge of a shed roof would include using a cupola to weather proof a hole in the roof or incorporating the same sort of ventilators that incorporated in domestic houses.

The ridge vent is one route for allowing the hot air to escape. Another route for allowing hot air in a shed roof to escape is through the use of a gable vent. This is basically an opening in the gable end of the shed roof which has louvres on it which act as a baffle to prevent wind-blown rain entering the building.

If the ridge and gable vents are the main routes that hot or damp air is directed out of the building.

How is cooler and drier air allowed to enter the building?

Cooler air is drawn into the building through vents that are in the soffits of the eaves, through the shed windows and doors and or drawn in through fans in the shed walls. Having these planned entry and exit points to control the flow of air into and out of the building brings up the question of what causes the air to flow through the building.

Air can be drawn through the shed passively or actively using fans.

Passive ventilation is what happens with most small sheds

The normal ventilation route of cool air being drawn in through the eaves vents and then as the air rises it escapes through the roof/gable vents happens naturally. If this passive ventilation does not happen fast enough then opening the door or window will help to let more cool air in flushing out the hot air from the roof.

The passive ventilation can be a bit hit and miss. The direction of the building in relation to the local winds, the strength of the local winds and also the local topography and distribution of trees and buildings can have a significant effect.

With more extreme climates and larger sheds the air flow sometimes needs a little help in the form of active ventilation.

With active ventilation the natural flow of air is given some help

Active ventilation gives the air flow a hand by either drawing in cooler air or flushing out the hot air at the top of the building.

Air can be flushed out using a whirlybird (rotating cowl) type vent. This type of vent is situated on the shed roof and is powered by the wind. The faster the wind blows the more air is drawn through the vent.

Alternatively powered fans can be used to give a more controllable flow, although these will need their own power supply and management system (could be as simple as an on/off switch).

The more air tight a shed is the more sophisticated the management system needs to be. In a large office type shed for example that is weather tight and occupied the whole year around then an air source heat pump might be used. This system would draw cool air into the building and then recover the heat from the warm stale air that it extracts so that minimum energy would be lost.

However by the sounds of it Mark the heat recovery system is a long way from what you are after.

Getting back to Marks question

I would say that the whirlybird type of vent would give this shed a good chance of venting the hot air out of the roof, with a bit more assistance than just relying totally on passive air flows. The whirlybird vent should be to remove the hot air from the top of the roof and so would not be required to be connected by ducting to the main space below. The hot air in the lower space would naturally rise up the building.

My concern here would be the lack of control in winter as you might then want to significantly reduce the airflow. So an alternative could be gable vents with powered fans. These vents could then be significantly reduced in winter so that the heat loss is controlled.

The insulation to the walls will help to reduce the heat gain in the summer and will also reduce the heat loss in the winter months ( You might like to have a quick look at this article on shed insulation ).

How do you intend to insulate the roof/attic? It would be worth looking into insulating the ceiling to the main space depending upon exactly how you intend to use the building.

Hope these thought are of use and please let me know how you get on.


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