Shed condensation: collect evidence before choosing a fix

Record the moisture pattern

Start with observations made from a safe position on the ground. Note the date, recent weather, whether doors were open and what was stored inside. Photograph the same areas when wet and dry. Identify whether moisture appears across much of the roof underside, along a particular sheet or below a penetration. Record the location of floor puddles separately from the location where water seems to originate.

Look for repeatable relationships without declaring a diagnosis. Moisture after rain may suggest rain entry, but the timing alone is not proof. Drips noticed on a dry morning may raise a condensation question, but stored moisture or an earlier leak can complicate the picture. The contractor needs a sequence of observations, not just the most dramatic photograph.

Do not climb onto the roof or remove linings to improve the evidence. Tell the contractor about inaccessible areas and any electrical equipment exposed to water. If there is an immediate safety concern, keep the affected area out of use and obtain appropriate professional assistance. A moisture log is useful preparation; it is not permission to investigate a hazardous space yourself.

Understand the condensation question

Condensation can occur when a surface is colder than the dew point of the surrounding air. Managing it involves the moisture present, surface temperatures and the ability of the building assembly to dry. Lysaght's condensation management bulletin explains those principles. Its housing provisions should not be copied as a shed specification; the designer must assess the actual building and use.

For an owner, the practical consequence is to avoid selecting a product before describing the problem. A roof coating, blanket, membrane or ventilator is not interchangeable with the others. Ask the proposed supplier what function the product performs and what conditions its performance depends on. Have those assumptions written into the scope.

Separate three goals in your brief: keeping rain outside, managing moisture within the building, and achieving the conditions needed by stored items or people using the space. One proposed treatment may address only part of that brief. Ask the designer to explain any remaining limitations so you can compare options on the same basis.

List wet activities and stored materials

Describe how water enters the shed through everyday use. Do vehicles arrive wet? Are damp covers, irrigation equipment or washed tools stored indoors? Is the floor cleaned with water? Is part of the building open to the ground? These questions do not establish the cause, but they give the assessor a more complete account than the phrase leaking roof.

Make a storage map. Mark sensitive tools, paperwork, timber, fabrics and electrical equipment, together with places where wet items are normally left. Note containers that are usually closed and areas that remain crowded. The purpose is to identify which items need protection while the cause is assessed, and which storage habits could reasonably change.

Be specific about activities planned for the future. A shed currently used for dry vehicle storage may later become a workshop with different moisture and extraction needs. Explain that change before ordering roof or wall work. If the building will house animals, crops, chemicals or another specialised use, seek advice for that use rather than treating this general storage guide as a specification.

Ask for a complete roof build-up

When comparing insulation or lining proposals, request a description of the complete roof assembly. Identify the cladding, any membrane or blanket, support arrangements, laps, junctions and the treatment around penetrations. Ask which products are being specified and obtain their current installation instructions. A quote that only says insulated roof does not explain what will actually be installed.

Have the contractor distinguish new-build installation from retrofit work. Some details are straightforward while the roof is being constructed but difficult to reproduce beneath existing sheets. Ask whether sheets need to be removed, what access is required and how the contractor will protect the contents. Clarify what happens to existing material that cannot be inspected until work starts.

Include maintenance access and later alterations in the discussion. Lighting, wiring or storage added after completion can interfere with the roof system if nobody understands how it was assembled. Keep product names and installation records with the shed documents. For a new building, coordinate this decision with slab and service planning so the roof and floor briefs describe the same intended use.

Specify the ventilation question clearly

Ask the designer to show the intended route of air through the building or roof space, identify the purpose of each opening and explain how the arrangement is expected to work. Avoid specifying a number of roof ventilators solely because another shed has that number. Give the designer the actual dimensions, internal divisions and operating pattern.

Explain practical constraints. Doors may need to remain locked when the property is unattended. Dust, insects, wind-driven weather and stored contents may affect which openings are suitable. A proposal that relies on leaving a roller door open all day may be incompatible with your security arrangements. Ask what performance is expected when doors are shut, because that may be the normal condition for much of the week.

If powered equipment is proposed, ask about control, electrical supply, noise, maintenance and replacement access. If a passive arrangement is proposed, ask how changes to shelving, partitions or linings might affect it. These are scope questions for the designer, not instructions to cut additional holes in existing cladding. Any opening must be coordinated with weatherproofing and the building system.

Compare retrofit disruption and uncertainty

For an existing shed, begin with the available drawings and a condition inspection. Note the age and type of roof if known, previous repairs and any alterations. The contractor may need to establish what sits above a lining or between layers before giving a firm proposal. Ask how that investigation will be carried out and what evidence it will produce.

Break each option into access, removal, preparation, installation and reinstatement. A proposal fitted from below may sound less disruptive, but the relevant question is whether it can deliver the required detail for your roof. A proposal involving roof removal needs a plan for weather exposure and contents. Compare the completed assembly and access requirements, rather than judging the options by installation method alone.

Discuss staging if the shed must remain partly in use. Identify areas that can be cleared, items that cannot be moved easily and times when machinery access is essential. Let the contractor determine a safe work sequence. A temporary storage plan belongs in the quote discussion, because contents left in place can restrict inspection and installation quality.

Example: moisture after wet equipment returns

This is an illustrative investigation, not a customer case. An owner notices droplets above a storage bay on several mornings and initially asks for the roof screws to be replaced. The observation log shows that wet equipment was parked in that bay before each event. Elsewhere in the shed, a separate stain appears below a roof penetration after wind-driven rain.

The owner gives the roofer both patterns instead of treating them as one fault. The inspection may find different causes, or it may reveal a connection not apparent from the ground. The written scope separates any weatherproofing repair from the assessment of internal moisture conditions. That makes it possible to judge whether both concerns have been addressed.

While the assessment proceeds, the owner rearranges suitable stored items away from the affected area without interfering with the building. The contractor advises on any necessary interim precautions. Follow-up observations use the same locations and record similar operating conditions. A dry day immediately after work is useful information, but it does not demonstrate performance under conditions that have not yet occurred.

Questions that make proposals comparable

Ask each contractor what evidence supports their diagnosis and what remains uncertain. Ask which part of the problem their proposal addresses, which products are included and which existing materials will remain. Request the relevant product documents and a sketch of important junctions. If a proposal depends on changes to how you use the shed, have those changes stated plainly.

Clarify exclusions that could affect the result. Does the scope include investigation of rain entry, removal of damaged material, electrical work, access equipment and reinstatement? Will the contractor inspect hidden areas once they are exposed? How will additional findings be recorded and agreed? These questions make a staged investigation easier to manage than an open-ended promise to stop all moisture.

Ask how completion will be checked. Installation photographs, product identification and a record of inspected details can be useful evidence. Agree what observations you should make afterwards and whom to contact if the same pattern returns. A written handover should explain the intended operation and care of the installed system without requiring the owner to guess what was done.

Keep a usable moisture record

Retain the original observations alongside the repair or improvement records. Continue noting conditions when moisture appears and when comparable conditions pass without a problem. Describe any changes in storage, cleaning, door operation or internal partitions. That context helps a contractor interpret later observations and avoids assuming that a changed building is being used exactly as before.

Use clear location names on the sketch, such as the bay beside the side door or the corner next to the tank. Photograph the same view where possible. Avoid relying on a pile of unlabelled close-up images; a wider image showing the position can be more useful than a detailed view with no reference point.

For a proposed farm shed or garage, discuss moisture management before choosing roof and wall details. For an existing building, the shed maintenance guide covers broader inspection topics, while this page provides a focused brief for the moisture problem. The next useful step is a documented assessment of the actual shed, followed by a scope that states what will change and how its performance will be reviewed.

Other moisture and storage topics

• General shed inspection and maintenance
• Workshop activity and storage planning
• Separate roof runoff and ground water issues
• Garage design and building options

Retain the wet and dry photographs with the contractor assessment. Compare the proposed work against each observed pattern and ask what follow-up will be needed.