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The role of building flood resilience within flood risk management
Andrew Tagg
Principal Engineer
Andrew Tagg
Principal Engineer
Page 2© HR Wallingford 2005 11 April 2023
Outline
Overview and definition of resistance / resilience
Research basis for new guidance
Guidance overview
Example of resilient home
Future developments
Page 3© HR Wallingford 2005 11 April 2023
Evolution of approach to floods
“Act of God” • Accept the vagaries of nature
Man against nature• Flood defence, control or management
Recognise social and environmental dimensions• “Living with rivers”
Flood risk management • A portfolio of policies and actions • “Room for the river” (NL, 2000)• “Making Space for Water” (UK, 2004)• New EU Directive (2007)
Page 4© HR Wallingford 2005 11 April 2023
Flood Risk Management Practice
Post-flood measures
Flood event measures
Real time risk management
Pre-flood measures
Preventive risk management
Forecasting and warning, reservoir control, evacuation, rescue, etc.
Spatial planning, contingency plans,
flood defence (mitigation) measures,
insurance, preparedness, etc.
Relief, clean-up, reconstruction,
regeneration, etc.
Page 5© HR Wallingford 2005 11 April 2023
Hierarchy of flood mitigation approaches
Definitions• Flood avoidance - constructing the building in
such a way that it avoids being flooded, e.g. by raising it above flood level
• Flood resistant - constructing the building to prevent flood water entering the building or damaging its fabric. This has the same meaning as flood proof
• Flood resilient - constructing the building in such a way that minimises water ingress and promotes fast drying and easy cleaning, and does not cause any permanent damage
• Flood repairable - constructing the building in such a way that although flood water enters the building, elements that are damaged by flood water can be easily repaired or replaced
Page 6© HR Wallingford 2005 11 April 2023
Research/responses for flood mitigation
• Flood avoidance - PPS25 and use of Flood Risk Assessments to determine flood risk and inform design
• Flood resistant - testing of flood protection products via kitemark scheme (to address doorways and other openings)
• Flood resilient - recent project to address other ‘weak points’ in walls, floors, joints
• Flood repairable - wide experience from flood repair industry (‘PAS64’, ‘Standards for repair’, ‘Repairing flooded buildings’)
Page 7© HR Wallingford 2005 11 April 2023
Recent project (1)
‘Improving the flood resilience of buildings through improved materials, methods and details’Funders
• DCLG & Defra / Environment Agency with:– NHBC– Scottish Building Standards Agency– Council of Mortgage Lenders– Concrete Block Association– CIRIA Core members
Page 8© HR Wallingford 2005 11 April 2023
Recent project (2)
Consortium• CIRIA• HR Wallingford• Leeds Metropolitan University• WRc• Waterman Burrow Crocker
TimeframeJanuary 2005 to February 2007
Contributes to ‘Making Space for Water’ (Defra)
Page 9© HR Wallingford 2005 11 April 2023
Resilience – main issues
Flood resilience• Limiting the damage• Reducing time to re-occupy• Health & safety issues – stress and the disruption
to normal lifestyle• Cost of repairs (Promoted by insurers)
Outcomes• A guidance document for key stakeholders• Methodology to incorporate methods and
techniques into the Building Regulations
Page 10© HR Wallingford 2005 11 April 2023
WP2 – Review of existing knowledge
• Reviewed experience and evidence from around the world • Very difficult to provide total flood resistance• Much of existing knowledge based on expert advice, assumptions and extrapolations • The advice is in the main derived from experience and a common sense approach• General lack of scientific experimental data• Little published scientific research into the performance of buildings and construction materials in floods, with only limited attempts to collect and analyse experiential data
Page 11© HR Wallingford 2005 11 April 2023
WP 6 (Collation & analysis of post-flood data)
• Many interviews with key groups/individuals involved in flood repair industry• Liaison with other initiatives (e.g. flood resilient house built as part of FLOWS project)• Review of new documents (PAS69, ‘Repair of flooded buildings’)• Analysis of drying data
• Largely confirms findings of WP2 review• Lack of hard evidence• Lack of agreement on definition of resilience
Page 12© HR Wallingford 2005 11 April 2023
WP5 – Laboratory tests
Testing programme:
• Stage 1 – Building materials • Stage 2 – Walls • Stage 3 – Floors • Stage 4 – Promising / Innovative materials
Page 13© HR Wallingford 2005 11 April 2023
WP5 – Laboratory tests of building materials
Test procedure (mimicking flood conditions)
Two phases:
- Wetting phase: up to 4 days (48 hours) ; testing units are exposed to still flood water 1m deep
- Drying phase: 7 days (168 hours); test units allowed to dry naturally under laboratory ambient conditions
Page 14© HR Wallingford 2005 11 April 2023
Elements testedMaterials Masonry cavity walls
Bricks: Engineering bricks (Classes A and B) Pressed Facing Bricks (sand and spike textured) Hand-made facing bricks
Empty cavity: Engineering bricks and concrete blocks Engineering bricks and Aircrete blocks Facing bricks and concrete blocks Facing bricks and Aircrete blocks Facing bricks and concrete blocks and external cement render
Blocks: Concrete blocks (3.5N and 7N) Aircrete (Autoclave concrete)
Full fill: Facing bricks and Aircrete blocks and mineral fibre insulation Facing bricks and Aircrete blocks and blown-in insulation Facing bricks and concrete blocks with mineral fibre insulation and internal lime based plaster
Timber board OSB2 11mm and OSB3 18mm thick
Part fill: Facing bricks and concrete blocks with rigid foam insulation
Mortars Below DPC 1:3 (cement:sand) Above DPC 1:6 (cement:sand)
Timber framed walls
Floors External facing bricks, empty cavity
External concrete blocks with cement render, empty cavity
External concrete blocks with lime render, empty cavity “Promising methods”
Thin layer mortar joint on solid block wall Solid masonry wall with external insulation Masonry cavity wall with external and internal renders
Concrete slabs (0.5m by 0.5m): 100mm thick, strength 32.5 150mm thick, strength 32.5 150mm thick, strength 42.5 150mm thick, strength 42.5, polythene sheet below slab - 300m overlap - Taped lap - Blockwork foundation, side wall - Blockwork foundation, side
wall, concreted trench - Blockwork foundation, corner
wall, concreted trench
Timber framed cavity wall using splash-proof plaster board
Page 15© HR Wallingford 2005 11 April 2023
Test results
Hand-made brick
Seepage through Hand-made brick
Page 16© HR Wallingford 2005 11 April 2023
Stage 2 - Testing of walls
Test rig – two identical test rigs
Page 17© HR Wallingford 2005 11 April 2023
Test results – illustrative examples
Wall ME1 (Eng Bricks on external face and Concrete blocks on internal face) during wet test
Plaster board
Page 18© HR Wallingford 2005 11 April 2023
Flood resilience characteristics
Water penetration – the seepage through the material (different from “water absorption”)
Drying ability – the capability to regain the original moisture condition
Retention of pre-flood dimensions, integrity – the lack of deformation or change in form or appearance of the material
Page 19© HR Wallingford 2005 11 April 2023
Summary information for GuidanceResilience characteristics*
Material Water penetration
Drying
ability
Retention of pre-flood
dimensions, integrity
Overall resilience
performance
External face
Engineering bricks (Classes
A and B)
Good
Good
Good
Good
Facing bricks (pressed: sand-textured, spike-
textured)
Medium
Medium
Good
Medium
Internal face
Concrete
blocks
Poor
Medium
Good
Medium
Aircrete
Medium
Poor
Good
Medium
Cavity insulation
Mineral fibre
Poor
Poor
Poor
Poor
Blown-in
Poor
Poor
Poor
Poor
Rigid PU foam
Medium
Medium
Good
Medium
Renders/Plaster
Cement render – external
Good
Good
Good
Good
Cement/lime render – external
Good
Good
Good
Good
Gypsum
Plasterboard
Poor
Not assessed
Poor
Poor
Lime plaster
Poor
Not assessed
Poor
Poor
* Resilience characteristics are related to the testing carried out and exclude aspects such as ability to withstand freeze/thaw cycles, cleanability and mould growth
Page 20© HR Wallingford 2005 11 April 2023
New Guidance
May 2007
Launched by Minister
Page 21© HR Wallingford 2005 11 April 2023
CIEF Bristol
11 December 2007
Design water depthup to 0.3m
Design water depthfrom 0.3m to 0.6m
Design water depthabove 0.6m
Approach
Attempt to keep water out‘Water Exclusion Strategy’
• Materials and constructions with lowpermeability
Allow water through property to avoid risk of
structural damage.Attempt to keep water out for
low depths of flooding
‘Water Entry Strategy’ ***
Design water depth* Mitigation measures
• Materials with low permeability up to0.3m
• Accept water passage through buildingat higher water depths
• Design to drain water away after flooding• Access to all spaces to permit drying
and cleaning
Attempt to keep water out, in full or in part, dependingon structural assessment.
If structural concerns exist follow approach above ***
• Materials with low permeabilityto at least 0.3m
• Flood resilient materials and designs• Access to all spaces to permit drying
and cleaning
Notes:
* Design water depth should be based on assessment of all flood types that can impact on the building
** Resistance/resilience measures can be used in conjunction with Avoidance measures to minimise overall flood risk
*** In all cases the ‘water exclusion strategy’ can be followed for flood water depths up to 0.3m
Remove building/developmentfrom flood hazard
Res
ista
nc
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Avo
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• Land raising, landscaping, raised thresholds
Page 22© HR Wallingford 2005 11 April 2023
Proposed changes to Building Regulations
New requirement in Part C* - Resistance to the effects of flooding:
• An FRA/FCA – mirroring requirements in PPS 25/TAN 15• Requirement to incorporate reasonable measures to
mitigate the effects of flooding• Adequate means of refuge/escape• Safe during floods without increasing risk to emergency
services• * Site preparation and resistance to contaminants
Page 23© HR Wallingford 2005 11 April 2023
Closing the loop between Planning and B. Regs.
Proposals to B Regs – expected to be implemented in 2008/09 – aim to close the loop between:
Planning system - key responsibility to determine whether flood effect mitigation is requiredBuilding control - responsible for its application
In practice, proof of compliance to amended Part C to be sent to LPA prior to commencement of building work
Page 24© HR Wallingford 2005 11 April 2023
Resilient House (1)
Page 25© HR Wallingford 2005 11 April 2023
Resilient House (2)
Page 26© HR Wallingford 2005 11 April 2023
Concluding remarks
• Await amendment to Building Regs. – will it happen?• Recent project on ‘encouraging uptake of resilience’• Pilot studies on resilience measures – update end May• Has new Guidance being used?
•Clear benefits from resilience, BUT- Needs incorporating into policy- Uptake for existing properties would provide greater benefits