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Social Housing Group Event
21stJune 2012
NHBC Standards
Chapter 7.2 ‘Pitched roofs’ 2012
Paul Cribbens
Chapter 7.2 ‘Pitched roofs’ 2012
Aims of this presentation
Reminder of why change was needed
What are the common causes of failure for roof coverings
What changes have been made in Chapter 7.2 2012
Be clear where to focus attention
Questions
Chapter 7.2 ‘Pitched roofs’ 2012
Claims performance – headline figures
More than 50% of all section 3 claims (by number) relate to
pitched roofs
Over 50% of all pitched roof claims involve mortar issues
We’ve seen that some builders are experiencing up to 70% of
all claims being related to pitched roofs
Pitched Roofs
Claims performance – Headline figures
More than 25% of section 3
claims costs relate to pitched
roofs
In 2009/10 annual claims
costs on roofs passed £10M
2010/11 costs in excess of
12m (and this only represents
cost of repairs to claims
undertaken by NHBC)
Is this the peak?
0
2
4
6
8
10
12
Co
st (£
m)
Pitched roof claims costs
Chapter 7.2 ‘Pitched roofs’ 2012
Review Chapter 7.2
Chapter 7.2 ‘Pitched roofs’ 2012
Mortar
Previous guidance asked for the mortar mix to be 3:1 sharp
sand/cement. Modified pre-mixed mortar was also acceptable.
3:1 sharp sand/cement is difficult to work and achieve a
reasonable finish. Modified mix or soft sand used due to
workability and availability.
Pitched Roofs
Mortar
Several winters have been
considerably colder than
average
Pitched Roofs
Mortar- Material failure
Chapter 7.2 ‘Pitched roofs’ 2012
Mortar, why does it fail
Mortar is asked to perform differently on roofs. Gap
filler and adhesive.
Roofs are generally the most exposed part of the
building.
Roof mortar connects materials with different thermal
expansion rates.
Modified pre-mix mortar, and soft sand mix has poor
tensile strength.
Chapter 7.2 ‘Pitched roofs’ 2012
Mortar- New Guidance
Roofing mortar should be 1:3 cement:sand with
plasticiser. The mix should be based on sharp sand
with soft sand added to achieve workability. The
proportion of sharp sand should not be less than 1/3 of
the total sand content.
Chapter 7.2 ‘Pitched roofs’ 2012
Mortar- New Guidance
Mechanically Fixed ridge and
hip tiles
Dentil tiles used where the joint
is in excess of 25mm
Chapter 7.2 ‘Pitched roofs’ 2012
Design out problems
Chapter 7.2 ‘Pitched roofs’ 2012
Designing out future
problems?!
Chapter 7.2 ‘Pitched roofs’ 2012
Dry systems
Around 40% of sites surveyed in
England and Wales currently adopt dry
systems, ridges were higher at about
60%
On sites surveyed in Scotland this was
higher, at over 90%
Is this relevant? Our claims figures
suggest a lower ratio of pitched roof
claims in Scotland compared to England
& Wales
Dry systems don’t remove all risk
but might be worth considering?
Ensure that components are installed correctly….
Chapter 7.2 ‘Pitched roofs’ 2012
ACTION
Ensure correct mortar mix is specified and used
Bed and point verges in a single operation
Consider whether dry systems may provide a better alternative
If dry systems are used, check they’re suitable and correctly
installed
Pitched roofs
Graded battens
Battens should be
marked in
accordance with
BS 5534
Pitched roofs
Small sections of cut tile
Guidance introduced to
prevent the use of small
sections of cut tile that are
difficult to fix
Typically found at abutments
and valleys
Pitched Roofs
Detailing of verges
Chapter 7.2 ‘Pitched roofs’ 2012
Detailing of verges
Battens should be set a
minimum 25mm-50mm back
Verge tiles should be placed
on a minimum solid 100mm
bed of mortar
Recommended overhang
for a verge is 38-50mm
(plain tiles) 30-60mm
(interlocking tiles)
Pitched roofs
2013 Guidance for verge tiles
At verges:
cut plain tiles are not acceptable and purpose made plain tile-and-
a-half should be used
small sections (less than a half width) of cut single lapped
interlocking tiles should not be used
natural slate verges should be formed with full slates and either
slate-and- a-half or half slates that are a minimum 150mm wide
all tiles and slates should be mechanically fixed at the verge in
accordance with Appendix 7.2-A
Questions?
