How to Tie in a Flat Roof Addition

Lead Image
  • 6-8 hours
  • Intermediate
  • 120-300
What You'll Need
Pry bar
Roofing cement

Tying in a flat roof addition makes it possible to extend and add to your existing property without affecting the look of it. If done properly, the flat roof can be tied in so that it doesn't change the look of the house at all. This will seal the parts of the roof together and reduce the risk of leaking.

Step 1 - Plan

To begin, carefully plan and decide how the two roofs will actually fit together. If both of the roofs are flat then they will normally butt up against one another, however, the problem with flat roofs is that there will always be a weakness down the center of the join. Most homeowners will have a pitched home that they wish to add a flat roof addition to. In this case, the methods used to tie the buildings together will be different. The methods used will differ even further if you are building a one- or two-story addition.

Step 2 - Single Story Additions

When building a single story flat roof addition on a two-story house the flat roof will normally simply butt up against the side of the wall. This makes it very simple however it does create a weakness in the design. Flashing must be applied along the gap between the flat roof and the brick wall to ensure that everything is watertight and secure.

Step 3 - Two Story Additions

If you are building a two-story flat roof addition then you will need to give this some special thought. The most problematic part of flat roofs is water pooling on the surface and gradually weakening the roof. This can quite easily result in leaks if it's not treated as quickly as possible.

Step 4 - Tie the Roof in

The roof needs to be tied in by lifting up some of the original tiles on the existing roof and then allowing the flat roof to run slightly underneath. After this roofing, cement is applied around the complete area and then the missing tiles are replaced. Flashing and more roofing compound are used to weatherproof the joint.

Also give some consideration to where the water will run. Water will cascade off your existing pitched roof but this cannot be allowed to pool on the flat roof. There needs to be adequate drainage in place to deal with this problem. Drainage needs to catch as much of this water as possible and put it down the drains where it can't cause any harm.

Step 5 - Maintain

Flat roofs are prone to leaking no matter how well you build them. Even modern roofs will be likely to leak at one time or another. You must regularly maintain your roof to keep it weatherproof and in the best condition possible.