2. Covering the roof
The structure is complete. Now you need to
keep the rain out and the heat in…
3. Roof coverings
• Pitched roofs
– Rely on gravity to move the water
down the slope
– Coverings keep the rain out by
overlapping
• Flat roofs
– Water may stand on a flat roof, so
the covering has to be completely
water tight.
4. Pitched roof coverings
• Can be anything from sheet lead
to thatch
• On new conventional houses, the
most common coverings are:
– Double overlap slates and plain tiles
– Single overlap interlocking tiles
• In both cases, coverings are
supported by battens on a “sarking
layer”
7. Sarking and battens fixed to each slope
Sarking layer, aka
underslating. Ideally
breathable but water
proof
Sarking should sag
between rafters and
project into gutter at
eaves
8. Sarking and battens fixed to each slope
Sarking layer, aka
underslating. Ideally
breathable but water
proof
Battens: softwood,
treated against decay.
Sarking should sag Nailed to rafters
between rafters and through sarking and
project into gutter at nailed to top of gable
eaves wall
9. Examples of battening out
This example is unusual. Sarking and
battening are normally completed before
slating starts. This is an old roof being
relaid under cover of a temporary roof
10. Slating. Vertical joints staggered, all slates double lap
Look at the text books
for details!
Every row is nailed to
a batten
Double overlap
11. Plain tiles: clay or concrete
Back of a plain tile:
projecting nibs hook over
the batten. Only every
third row needs to be
nailed
12. Interlocking tiles: clay or concrete, single overlap, much lighter
The edge of one tile
overlaps and
interlocks with the
edge of the next
13. Ventilate the roof through the eaves and ridge
Essential to maintain ventilation of
the enclosed roof space to avoid
condensation
14. Ventilating the slope and ridge
• The sarking
must be pierced
to allow the free
flow of air but
protected from
rain penetration
• Special tiles can
do this at the
ridge and in the
slope.
15. Free flow of air within the roof space above ceiling insulation essential
Ventilated ridge
Slope ventilators
Eaves ventilation
17. Basic insulation of a pitched roof
Fibreglass insulation
laid between joists.
300mm recommended
18. Basic insulation of a pitched roof
Fibreglass insulation
laid between joists.
300mm recommended
Vapour barrier on
warm side
19. Basic insulation of a pitched roof
Fibreglass insulation
laid between joists.
300mm recommended
Vapour barrier on
warm side
Free flow of air
essential
20. Flat roof coverings
Firring piece on each joist
facia Roof deck and finish
to create fall to gutter
Roof joists at 600mm centres
soffit
• Flat roof coverings
on the deck can be:
– Sheet material,
bonded to the deck
– Hot or cold liquids,
which cure to form a
skin. (Only really
applicable to a solid
concrete roof deck)
21. Sheet roof coverings
• Bituminous felts laid in hot adhesives
(tar)
– Usually in three layers, finished in gravel or
paint to protect from UV radiation
• “High Performance” roofing felts on hot
tar
– Usually two layers. Flexible and self finished
• Loose laid reinforced uPVC fabrics,
glued to points on the deck. Not
common in housing
22. Alternative felting systems
Base layer being unrolled Detailed work around
into hot tar edge
Hi performance top layer Torch-on system Self adhesive Hi
being laid performance felt
23. Insulating a flat roof
• This is one of the difficult areas
because of the limited volume
inside the roof
• The two main systems are “warm
deck” or “cold deck”
• The important thing is to prevent
condensation inside the roof space
25. Cold deck principles: ceiling void is cold and ventilated
deck
roof void
ceiling
Roof finishing layers
Insulation between joists
Vapour barrier
Void must be ventilated from the eaves
Very difficult to achieve in practice
