PDF DOWNLOAD WITH GUIDES HERE: www.rebu...ldchr...stchurch.co.nz/.../...7a0b1.pdf
WHAT GUIDELINES DOES IAG USE?
IAG uses the guidelines issued by the Department of Building and Housing (DBH) in its November 2011 document Revised guidance on repairing and rebuilding houses affected by the Canterbury earthquake sequence.
This document includes guidelines for assessing the damage caused to a house, based on floor levels within the house, to assist in the overall decision process of whether the house can be repaired or needs to be rebuilt.
The Christchurch City Council, Selwyn District Council and the Waimakariri District Council have accepted the guidelines.
WHY WERE THE GUIDELINES CHANGED?
In early 2011, members of the DBH’s Engineering Advisory Group surveyed brand new concrete floors, undamaged by earthquake activity.
The engineers found that a typical, new concrete floor could be built with a slope exceeding the 0.25% limit (5mm over a 2 metre distance) contained in the DBH December 2010 guide. This meant that under the original guidelines, a new slab constructed in accordance with New Zealand Standards could be assessed as needing to be repaired, although it had not been damaged in any way.
The engineers also found that the instruments used to measure floor levels are accurate to within 3mm. An example of this variance is that a floor, which measured at an 8mm slope, could in fact actually have a slope of either 5mm or 11mm.
After also taking into account that all buildings naturally settle and move over time, the Engineering Advisory Group concluded that floor levels could typically vary by up to 50mm over the entire area as a result of construction tolerances and settlement, without having any noticeable effects on a house.
Based on this conclusion, the DBH decided to issue revised guidelines for repairing and rebuilding earthquake-damaged properties.
I WAS ORIGINALLY TOLD MY HOUSE WAS LIKELY TO BE A REBUILD, WHY IS IT NOW A REPAIR?
Between December 2010 and November 2011, [IAG] assessed houses against the originally developed DBH guidelines, which contained different floor level criteria to the revised criteria.
Under the previous guidelines, a house with only relatively minor floor level differences may have fallen into the foundation rebuild category, instead of the re-levelling category.
This may mean that a decision to rebuild a house based on an assessment done before November 2011 could change, because the revised guidelines now reflect the ability to repair the house, rather than unnecessarily demolish and rebuild it.
THE NEW DBH FLOOR LEVEL AND FOUNDATION RE-LEVEL CRITERIA
No repair needed
If your timber or concrete floor has:
less than 50mm overall difference in level and 0.5% slope between 2 points greater than 2m apart; and
no serious cracking.
Foundation re-level needed
If your timber floor has an overall variation in level of between 50 – 100mm; or
If your concrete slab has an overall variation of 50 -150mm; and
It has no serious cracking.
Foundation replacement needed if:
your timber floor has an overall variation in level of more than 100mm;
your concrete slab has an overall variation of more than 150mm; or
there is significant cracking to floor or foundations.
The guidelines also suggest that the serviceability of areas is taken into account in deciding whether a floor needs to be re-levelled or foundations replaced.
A bathroom floor now slopes 10mm; however, the water is now running away from the drain. In this case, the floor would require repair because although the floor level is within the allowable levels, the lack of drainage makes the area unserviceable.
The floor slopes 55mm over the entire length of the house, with no serious cracking. Although this is above the 50mm guideline, it is possible that the floor does not need to be re-levelled, as the integrity of the house is not affected.
The relevant criteria from the revised DBH guidelines are attached for your information.
Extract from ‘Revised guidance on repairing and rebuilding houses affected by the Canterbury earthquake sequence’ DBH: November 2011, www.dbh.govt.nz/guidance-on-repairs-after-earthquake