The following is a guide to laying felt roofing with adhesive to a timber roof deck built with OSB or plywood boards. This method is for flat roofs for outdoor structures such as garages, summer houses, workshops, sheds or log cabins.
- Ensure ambient temperature is between +3 and +27°C
- 1l per 1m2 of adhesive such as IKOpro Roofing Felt Adhesive
- Felt underlay
- Seal any gaps between the roofing boards with
- Starting from the lower edge of the roof, roll out a length of felt underlay horizontally across the roof plane and cut to size leaving 50mm overhang at both ends and a 750mm eaves overhang at the front edge.
- Work your way up the roof rolling out successive lengths of underlay felt overlapping the top edge of the previous length by at least 750mm until you reach the top edge.
- Roll up the cut felt sheets and place them to one side.
- Ensure that the roof surface is clean, dry and free from grease, oil, dirt and loose material. Use a soft brush and acetone to clean if required.
- Starting from the lower edge of the roof, cover the roof with rows of 100mm wide strips of adhesive horizontally across the roof plane leaving gaps of 100mm between each strip.
- At lower roof edge, roll out the first sheet of felt underlay across the roof, over the adhesive, keeping it square and flat. Press out the sheet with a broom or roller.
- Fix the sheet with 20mm large head galvanized clout nails, staggered at 150mm centres in both directions.
- Roll out successive lengths of underlay felt on the the roof adhesive giving at least a 750mm overlaps. Apply adhesive to each overlap joint and then fix each sheet with nails at 50mm centres.
- Once the roof is covered completely with the underlay, cut the first top sheet (or intermediate sheet if applying more than two layers) to size ensuring that it is half the width of the underlying felt so that the overlaps are not on top of one another.
- Continue laying the top sheets in a similar fashion to steps 2 to 3 above ensuring that they overhang by 750mm at each end and that the lower and higher edge of the roof is overhung by 750mm. Set the sheets to one side.
- Brush or roll the entire roof surface with adhesive and allow to cure for around 15 minutes until tacky.
- Starting from the lower / gutter roof edge, unroll the top / intermediate sheets across the roof ensuring that they they are aligned properly ensuring 750mm overhangs around all roof sides.
To obtain a clean finish to top sheet laps, the cold applied adhesive should be carefully spread so that there is no surplus beyond the finished edge of the lap.
Membrane upstands and detail work should always be formed with separate pieces and be fully bonded in roofing felt adhesive.
Upstands to brickwork etc. should finish beneath a lead flashing, or be dressed into a chase in the mortar joint.
When the adhesive is nearly dry (approx. 6 hours) the roof should be inspected and any sections not adhering properly should be firmly pressed or rolled down.