Building Report Canberra ACT

ADVANCED STRUCTURAL DESIGNS

Block ? Section ?

ARANDA

Canberra ACT

Structural Audit

on behalf of

???? ??????

May 2002

Job Number

2004

Prepared by:

Advanced Structural Designs Pty Ltd

91 Banambila St

ARANDA ACT 2614

Telephone: (02) 6161 2171

Facsimile: (02) 6161 2170

1.0 INTRODUCTION

At the request of ???? ??????, Advanced Structural Designs were commissioned to undertake a review of the building structure described on the cover page. The purpose of the review was to inspect the structural condition of the building and to comment on its structural integrity, likely future performance and suitability for future extensions. .

The review undertaken was limited to a walk through inspection of the building and a review of the “as constructed” drawings lodged with BEPCON that were supplied by the owner.

2.0 DESCRIPTION OF BUILDING STRUCTURE

The building has a flat steel roof falling at a pitch of one degree toward a box gutter on the north of the building. The steel roof is supported an varying height battens (fall battens) which are supported by 220*65 dressed Oregon rafters which appear to be continuous in length and are supported by internal and external walls. The oregon rafters are exposed throughout the house. The external walls and some internal walls are constructed of 190mm concrete blockwork and one internal feature wall is constructed of single skin clay brick masonry. Walls are directly supported on 450mm wide by 230mm deep strip footings and the floor is a 100mm thick slab on ground.

The adjoining carport is constructed from oregon beams and posts supporting a flat steel roof falling at 1 degree towards the west (street front).

3.0 BUILDING INSPECTION

A site inspection of the building was carried out by Advanced Structural Designs on 3^rd May 2002. This visual inspection involved a walk around the building paying attention to and photographing items such as cracking brickwork, rotting timber or cracks in slabs.

During the inspection the following notes were taken

1 Cracks in the brickwork are prevalent in various areas around the building (see photos) and generally vary in size up to 0.7mm except for a crack in the courtyard wall which is 15mm wide (photo 16) but hidden from view due to surrounding shrubs. The cracks are particularly evident adjacent to openings and occasionally stepped to mirror the mortar beds and perpends. Cracking is also evident under the timber beams when the beams rest on brickwork supported by steel angle lintels over the window openings.

2 The oregon joists are 9.5 metre long and continuous in length but they are often rebated 5 to 10 mm over support walls (see photo 13). They have smaller dimensions to those shown on the original drawings with the difference being consistent with the dressing of the timber and its subsequent shrinkage. The timber is displaying some checking (near horizontal cracking) which is normal for the species and of no concern.

3 The posts supporting the garage are oregon and have rotted to the point that they have now past their serviceable life. We suggest that these be replaced as soon as possible preferable with a more durable species such as cypress or silvertop ash. We estimate the cost for this work to be less than one thousand dollars.

4 The house fascias appear to be hardwood and are in reasonable condition but in need of painting. There are some early signs of decay adjacent to the gutter overflows but these areas should last for another 4 to 5 years provided the gutters are adequately maintained. When the areas do need to be replaced the repair can be confined to the problem areas and should cost less than $1500.

5 The roof is in poor condition with widespread rusting. This condition is patly due to the very flat fall which is ponding water in some places. We saw some evidence of roof leaks during the walk through inspection and recommend that the roof be re-levelled when it is replaced. We advise that the roof would need to be replaced within the next 5 years at an approximate cost of $18, 000.

4.0 REVIEW OF THE EXISTING DRAWINGS

A review of the current copy of the existing house drawing revealed that there are no unapproved structures on the property and that the construction of the house appears largely consistent with the drawings.

5.0 MASONRY CRACKING DIAGNOSIS AND RECOMMENDATIONS

The cracking to the masonry walls, although widespread is minor in terms of severity and there is no evidence to suggest that the structural integrity of the building is compromised. Around 80 percent of the cracking is the direct result of blockwork shrinkage although 2 or 3 of the cracks do exhibit some evidence of foundation movement (see photo 18).

The foundation movement is a little surprising on this site given the nature of the local geology as the depth to rock is normally relatively shallow in this area. The large crack in the courtyard wall is the result of upheaval of the footing by the root system the adjacent eucalypt (see photo 16).

We recommend no action be taken to address any cracking from a structural perspective but if cosmetic solutions are desired options would include filling with flexible sealants or cutting in control joints.

6.0 POTENTIAL TO EXTEND OR ALTER THE EXISTING STRUCTURE

As mentioned above, the cracking to the external walls is mostly shrinkage related but there are two or three cracks that have a component related to the shrink swell movement in the soil. The additional of another level in masonry is not recommended given the performance of the footing to date and we recommend any additional floor should be of lightweight construction with timber or fibre cement cladding.

If a masonry clad second floor was a strong preference it would be possible to reinforce and core fill the blockwork on both the lower and upper floors to overcome the footing inadequacies but problems such as thermal bridging would also need to be considered.

The advice you have received from your builder regarding the internal walls being non loadbearing is for the most part incorrect. The rafters although continuous for the full span, are only capable of spanning around 5 metres and are always supported on internal walls as well as external walls. If internal walls are removed the rafters will need to be supported some other way. One other point worth considering is that the rafters are often rebated 5 to 10 mm over support walls which will be unsightly should you choose to move the alignment of the support walls to some other location.

In the past when removing load bearing walls on this type of construction we have added timber beams of similar depth in the same plane as the rafters and directly over the location of the old wall (see detail 1 appendix B). These new beams could be expected to span around 4.5m if you where to specify reclaimed seasoned hardwoods.

5.0 OTHER POINTS OF INTEREST

The use of single skin blockwork for external walls is relatively unusual in Canberra and it is worth noting the following points;

1. In situations where the inside of the residence undergoes a relatively rapid rise in heat and humidity the walls can become damp. This phenomenon is known as thermal bridging and although this type of construction performs less well than brick veneer in this respect it’s performance is superior to the monocrete construction prevalent in the inner southern suburbs

2. It is important to maintain the waterproof paintwork on the walls that are not protected by an overhang such as those on the east and west faces of the building if you are to avoid damp internal walls during prolonged wet spells.

3. The insulation value is relatively low (R=0.34) which can lead to greater heat loss in winter (or gain in summer) than say an uninsulated brick veneer home (R= 0.45) or double brick homes (R=0.5). To keep this point in context all new homes in the ACT are required to have an R value of 1.5 in the walls which is far in excess of any of the above. While brick veneer and double brick homes can be effectively insulated at a later date for this type of construction insulation is more difficult to achieve and far less effective.

7.0 CONCLUSIONS

The building structure is in fair condition for its age except the roof and the garage support posts, which are nearing the end of their useful life.