On bituminous flat roofing, an upstand reinforcing strip is an extra strip of membrane in the corner where the roof surface turns up against a rising element — a roof edge, a wall or a parapet. The strip runs about 15 cm out onto the roof surface and is then taken up the upstand, so that this vulnerable corner is built up in two layers instead of one.
The Dutch word for it, kimstrook, has a second meaning in masonry: there it is a synonym for the levelling course, the first course of bricks or blocks in a wall.
Why the extra strip is needed
The change from horizontal to vertical is the most heavily loaded spot on a flat roof:
- Movement — the roof surface and the upstand move against each other with temperature changes, and that movement concentrates in the corner
- Water — rainwater running towards the roof edge or a parapet stands here the longest
- Folding — a membrane bent through a sharp corner is at its thinnest there and fatigues faster
- Snow and dirt — against a wall, dirt collects and keeps the membrane damp for longer
A single layer in a sharp corner is therefore a risk. The reinforcing strip turns the corner into a doubled, strengthened zone.
How it is done
- Prepare the corner — an angle fillet of timber or insulation is usually fitted, so the membrane makes a 45-degree transition instead of a right-angled kink
- Fit the strip — bond or torch it fully, about 15 cm onto the roof surface and high enough up the upstand
- Membrane over the top — the main roofing layers are then run over the strip
- Finish the top edge — the upstand is mechanically clamped at the top and capped (edge trim, flashing or coping profile)
Points to watch
- Upstand height — keep the height the roof detail specifies; too low means water can go over the edge in heavy rain or with a blocked outlet
- No right-angled kink — a membrane turned sharply without a fillet will split there in time
- Fix mechanically — a membrane must never hang on adhesive alone at an upstand; the top edge has to be clamped
- Fire safety when torching — working with an open flame near timber, insulation and cladding calls for strict precautions, so many details are done self-adhesive or with hot air
Related terms
- Levelling course
- Flat roof
- Bitumen
- Roof covering
- Wall-floor joint
- Gutter
Want to learn more about construction terms? Visit our knowledge base at fredsdiyplans.com.