How do you attach a pitched roof to a flat roof?

Answered by Phillip Nicastro

To attach a pitched roof to a flat roof, there are several steps that need to be followed. Here is a detailed explanation of the process:

1. Prepare the flat roof: Before attaching the pitched roof, it is important to ensure that the flat roof is in good condition and properly prepared. This includes checking for any leaks or damage and repairing them as necessary. The surface of the flat roof should also be clean and free from debris.

2. Strip the tiles and battens: Carefully remove three courses of tiles from the adjoining roof where the pitch will be attached. This can typically be done by lifting the tiles and sliding them out from under the battens. Once the tiles are removed, the roofing battens can be taken out as well.

3. Install the underlay: Lap the roof underlay over the top of the EPDM (Ethylene Propylene Diene Monomer) membrane, which is commonly used as a waterproofing material for flat roofs. The underlay should be laid in such a way that it provides a continuous barrier against any water infiltration. It is important to ensure that the underlay is securely fastened and properly sealed to prevent any leaks.

4. Reattach the battens: After the underlay is in place, the tile battens can be reattached. The battens should be fixed onto the roof structure securely, using appropriate fixings such as screws or nails. It is important to ensure that the battens are level and straight, as they will provide the support for the tiles and help maintain the pitch of the roof.

5. Position the EPDM membrane: The EPDM membrane should be positioned so that its top edge is at least 300 mm (12 inches) up behind the bottom of the lowest tile. This will provide a sufficient overlap between the pitched roof and the flat roof, ensuring that water does not penetrate the joint.

6. Install the pitched roof: With the EPDM membrane in place, the pitched roof can be installed. This typically involves laying the roofing felt, installing the battens, and then fixing the tiles onto the battens. It is important to follow the manufacturer’s instructions and best practices for installing the specific type of pitched roof being used.

7. Ensure proper drainage: As the pitched roof is being installed, it is important to ensure that proper drainage is maintained. This includes installing appropriate gutters and downpipes to channel water away from the roof and prevent any pooling or water damage.

Throughout the process of attaching a pitched roof to a flat roof, it is important to prioritize waterproofing and proper installation techniques. This will help ensure that the roof is watertight and able to withstand the elements. It is recommended to consult with a professional roofing contractor for guidance and assistance, especially for more complex or large-scale projects.