How to repair leaking roof?

HomeHome Improvement

  • Author Kc Ang
  • Published May 20, 2022
  • Word count 1,406

Roof leaks can cause interior damage to your property. Fortunately, there are several items available to assist in keeping the weather out. Repairing roof leaks is simple, but pinpointing the source of the leak may be tricky. Because water can move along the undersides of beams and seep between layers of roofing material, the moist patch does not necessarily appear precisely underneath the leak. Rather of leaping to conclusions, eliminate all probable causes one by one.

Detecting leaks

A flat roof is the most difficult site to discover leaks. The only remedy is often to thoroughly treat the roof with a waterproofing solution. The work of detection should be easier on pitched roofs since slipped slates and tiles may be identified from the outside. Remove and replace cracked tiles by carefully moving them away from the nibs they are resting on. Inserting wooden wedges under the overlapping tiles might sometimes assist. Every year, examine your roof using binoculars.

Chimney stack leaks are notoriously difficult to detect. Rain seeping in from the top is the most obvious culprit, as are leaking flashings allowing rain in around the sides. However, this may not be the case. Condensation within the flue is frequently the source of wetness. By the time this is detected, a considerable amount of time, effort, and money may have been used on sealing the flashing and capping the pots.


Condensation will occur if moisture vapour from the home is confined in an unventilated location. This can happen in lofts, abandoned chimneys, or above flat roof ceilings. Flat roofs must have adequate ventilation to prevent airborne moisture from entering the space above the insulation and below the waterproof felt. When moisture accumulates, it causes damp spots on the ceiling and blisters in the roofing felt.

Disused chimneys must be vented using a bottom air intake and a top output. If this is not done, airborne moisture from the home will enter the chimney and condense on the cooler interior. As a result, moisture and soot are dragged through the brickwork, resulting in wet spots on the chimney breast. The loft insulation being pushed back to keep the loft aired causes a chilly spot in the corner of bedrooms with sloping ceilings. In other circumstances, the short sloping area of the ceiling may have no insulation at all, making it a natural spot for condensation to accumulate. One method of preventing condensation is to improve ventilation with extractor fans or a dehumidifier.

Flat felt roofing

Roofs should never be level. The water should drain fast. Low places and puddles If water accumulates in one area on the roof, it is likely to seep through. Create a short portion of new roof over the old one if you can’t cover the low sections with trowelling-grade mastic or build it up with two or three layers of felt. Use a sheet of polystyrene bitumen adhered to the existing felt. Plywood should be used to cover the top of the felt, and felt should be laid over the plywood. Make sure the felt extends down the sides and at least 150mm onto the roof. Use cold-lay adhesive or hot mastic to adhere the felt to the existing roof.


If you have minor blisters on a flat roof that aren’t leaking, leave them alone and use a solar- reflecting coating to keep the surface cool throughout the summer. If the felt has broken or appears to be about to break, it must be mended. To make envelope flaps, cut four diagonal lines in the felt. Peel back the felt gently to reveal the beneath layer of roof decking. Apply a large layer of felt glue and press the cut edges into it, squeezing away any excess. Use galvanised felt nails, sometimes known as clout nails, to secure the flaps. When this layer is dry, add extra glue and put a felt patch over the top, overlapping the repair by 150mm on both sides. Place some slabs on it for a few days to help it cling. Flashing repair tape can be used to cover flashing and connects to vertical up stand. When putting it in place, make sure you apply enough pressure to get rid of any trapped air underneath.

Stopping heat damaging felt

In the summer, dark coloured felt will absorb a lot of heat, and if the flat roof has insulation below, the heat will only escape upwards. To combat this, white stone chipping are frequently utilised to reflect sunlight. The issue with chipping is that if someone walks on the roof, the chipping might press through the felt and produce leaks. Another method of safeguarding the felt is to use solar-reflective paint, which is specially designed for this purpose. A single coat of paint can be applied using a brush or a roller. The use of solar-reflective paint will lengthen the life of any flat roof, whether it leaks or not.

Applying waterproofer

Waterproofers are available in water-based emulsions for use in fine weather and solvent-based paints for use in the winter months or when it seems that it may rain before the coating is finished. Before spraying waterproofer, use a fungicide and moss killer to remove any indications of algae and moss from the roof. Killing the roots might take many days. Apply the first application of waterproofer after brushing the roof with a strong broom. When applying a bitumen emulsion, it is essential to dip the brush in water every now and then to increase the flow. Apply a second application in the other direction once the first coat has dried.

Laying new felt

Use a high-performance polyester felt when re-felting a portion of your home. When felting a shed or garage, you can utilise less expensive conventional felts. These do not apply. Three layers of felt are traditionally layered on top of each other to feel a roof. Each layer must begin at the bottom of the roof so that the laps are stepped in the proper direction to shed rain on the following sheet. The initial layer over timber decks should be nailing preparation-layer felt developed specifically for this purpose. Check that the joints in each layer are not immediately above one another.

They should be separated by at least 150mm. Apply a continuous coating of hot bitumen or cold-lay adhesive on the second layer of felt. Cut felt strips to place over the top of the horizontal layer and up the wall where the roof meets a vertical wall. Then, place a piece of felt or flashing into a chiseled-out mortar joint in the brickwork. If you can’t do this, cover it with mending tape.

Mastic sealants

Gun-applied mastic sealants can be used to adhere roofing felt edges and reseal flashings around chimneys. Check that the surfaces to be adhered to are clean and dry. Hammer short strips of lead into the brick courses to wedge loose flashing. Cover splits and gaps using flashing repair tape.

Using self-adhesive roofing felt

Install a two-layer self-adhesive high-quality roofing felt. Once laid, the heat from the sun helps to adhere the felt to the ground. Check that the surface is clean and dry. To shed water, the roof board should be ran on a slope. Use triangular wooden fillets around the margins of walls to keep the felt from running into an acute corner.

Using a brush or roller, apply the sealer/primer to the roof board

When the first layer of felt is dried, apply it to the roof. Roll back halfway and cut the backing paper to remove it. As you remove the paper off, gently stomp the felt down. When the first half is adhered, adhere the second half, followed by the drip edge pieces. These will flow over the roof’s edge and into the gutter. They should be fastened facing down and folded upwards to create a double thickness drip over a wooden batten (8). Look at a few flat rooftops in your region if you’re not sure how this is done.

After the drip edge has been installed, the top layer of felt may be laid down over the previous felt. Stagger the second layer connects so they are not in the same position as the first layer joins. If you’ve lapped felt over the green mineral treatment, fill the granular surface with mastic so the felt has an even bed to cling to.

We are a waterproofing company that specialises in roof waterproofing, walls waterproofing, floor waterproofing, basement waterproofing, bathroom waterproofing and water seepage/leakage repair.

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