Roof Waterproofing

The biggest difference is whether one spot is fixed or the whole roof is redone. Resealing one joint or drain outlet on a roof that is otherwise sound is a small job. Coating a whole roof is bigger, and bigger again when the old layer has to come off first. Sika's data sheet for its Sikalastic-590 coating, for example, says an existing coating must be sound and firmly stuck down, and the surface below 6% moisture, before the 590 goes on, so a lifting or damp layer means stripping or drying work first. A tiled roof terrace adds lifting and relaying the tiles to reach the waterproofing underneath. Fixing a drain outlet or a slope where water stands adds work, and so does a roof that is hard to reach. Roof waterproofing costs for repair, recoat or replacement go through these in more depth.

Leave the roof to the contractor, because getting up there is work at height, and look and take notes only from inside the house or from a safe window. Catch the drips, move belongings out of the way, and keep clear of any light fitting or socket that is getting wet until an electrician has checked it. Take photos of the stain and the drip, note when it leaks (in heavy rain only, or every time it rains) and which rooms are affected, and send those to us with your enquiry. A temporary cover over the leaking area and the permanent repair are separate pieces of work, and the cover only buys time. What to do while you arrange help has more, and five signs a roof needs waterproofing covers the marks that show up before a drip.

Only if the new coat covers the place where water is getting in and goes onto a sound surface. If the leak comes from the joint where the roof meets a wall, from a drain outlet or from damp trapped under the old coating, another coat over the main flat area leaves that route open. A leak that comes back after recoating suggests the entry point may not have been found. If the last job came with a written warranty, start the warranty claim before paying for another coat.

The one that suits how the roof is used and what is on it now. For an exposed flat roof with plenty of pipes and corners, a liquid acrylic or PU coating forms one seamless layer, and Sika lists roofs with numerous details among the uses of its SikaRoof PUR-18. A roof that will sit under tiles or a garden needs a system that can be covered, such as a torch-on sheet. If water still stands on the roof long after rain, ask whether the fall or the drain outlet should be corrected in the same job. Sika recommends a 1% fall for its Sikalastic-590, with 0.5% possible as a minimum depending on the roof layout and drains, and says the 590 can go on roofs with short ponding water, while it rates PUR-18 for standing water but not for sitting under water permanently. Choosing waterproofing for your roof and torch-on versus liquid waterproofing go further.

It can, with a system made to sit under a finish. A coating made to stay exposed is not automatically suitable, and Sika says its Sikalastic-590 is an exposed system that must not be covered with tile or concrete. Sika lists rooftop gardens and patio decks among the uses of its SikaShield P24 torch-on sheet. On an existing tiled terrace, redoing the layer underneath means lifting the tiles, and the drain outlets and the upturn at the walls are redone with it so the new layer joins them. Exposed versus screeded roof waterproofing compares the two set-ups.

No single number holds across products, so a lifespan quoted for a whole type of waterproofing tells you little about your roof. What shortens it is easier to pin down. Water left standing on a product not made for it is one, since Sika rates its SikaRoof PUR-18 for standing water but not permanent immersion. Covering a coating made to stay exposed is another, and Sika says its Sikalastic-590 must not be tiled over. Coating over a damp or loose surface is a third. A written warranty, if one is given, is the firmer promise. Check who gives it, which area and work it covers, what the remedy is, what it excludes and what upkeep it requires, including what happens if later equipment work disturbs the roof. Roof waterproofing warranties are explained in more detail.

Not on a wet surface, for the products on this page. Sika's data sheet for its Sikalastic-590 coating asks for no water, moisture or condensation on the surface, rates a fresh coat as rain resistant after about 6 hours at 30°C in its test conditions, longer in high humidity, and says to keep rain off it for 24 hours for good resistance to standing water. Its SikaShield P24 torch-on sheet also goes onto a dry deck. When rain stops the work, the open areas are covered and the surface has to be dry again before the next coat. Planning roof work around the weather goes further.

That comes down to which rooms sit under the work and how the workers reach the roof. The rooms directly below the part being stripped are the ones exposed while the old layers are off, and if there is no outside access, the stairs or room the workers pass through will see traffic, noise and dust. Before anything is stripped, agree which rooms are cleared or covered, how the open roof is covered each night and when rain stops work, and who puts those covers up.

It depends on what the work involves, and a Qualified Person is the one to say. BCA says private property owners should engage a Qualified Person, a registered architect or professional engineer, to advise on the clearances needed from BCA and other authorities for the building works they plan. If your house is in a strata-titled development, BCA notes the MCST's approval might also be needed, and who arranges roof repairs differs between condos and landed homes. Roof waterproofing and approval has more.