Building Inspections


Introduction

The world is built on the efforts of private enterprise where the natural desire is to maximise profits by charging the highest price the market will bear and by minimising costs.
An important regulatory factor as that aspect of activity described as quality.


Good quality products earn a better reputation than poorer quality products. Yet, there are those who will put a fine exterior on a product and use low quality materials and methods where things are hidden from view.
A second regulatory factor is that of safety. For many products safety is of minor consideration whereas for others it is a very important consideration. In housing safety of the structure and its occupants in the long-term is important yet it is an aspect that may be neglected through expediency or genuine lack of knowledge.
The level of available knowledge throughout the world varies from country to country. In the building industry those countries where the climate is windy or prone to regular hurricanes, and have a developed economy, the level of knowledge in methods of safe construction are highest. In other countries certain areas of knowledge are not relevant. It is incumbent upon those who have a statutory responsibility for regulation and its administration to ascertain the relevant knowledge and to embody it in the relevant regulatory codes.
Codes in themselves are an important basis for the establishment of required knowledge but they also need accompanying methods of education and inspection.

Building Plans and Permits

A fee schedule needs to be established which will generate sufficient income to cover the costs necessary to pay for all aspects of

Plan Approval

This is a very important procedure. Plans need to be inspected to see that they comply with 2 main things

Once a plan is approved a permit for the construction should be immediately issued.


A Building Inspection Regime

This has 10 main components

In addition to what is detailed here general compliance with the Code may be checked at each inspection. What is detailed here are the most critical items which must be inspected at the correct point in the construction programme.

They are generally aspects of construction which will be covered up at the next step.

For instance, reinforcing will be enveloped in concrete and become generally invisible when the concrete is poured.
Utilising this concept it is possible to design a building inspection system which revolves around a series of inspections at critical points in a building's construction.
A series of inspections along the following lines is generally adequate for residential construction. Commercial and Public Building construction can follow similar lines but may require a custom designed inspection regime depending on the particular project.

Foundations

Make an inspection when the foundation trenches have been dug, boxed and the steel placed ready to pour the foundation concrete.



Concrete Floors at Ground Level

Prior to the pouring of Concrete



Walls


Framing

Timber Framed

Window and Door Lintels Timber framed with block or brick veneer Cladding


Timber framed



Concrete walls

Block

Where these are structural then they will need to be filled with concrete with appropriate steel in those cells designated as columns and in the specified horizontal bond beams.

Pre-cast Concrete (Sections of walls)

These may come in a range of sizes. Some may interlock to give larger panels which fill spaces between columns. Others may come as units which fill spaces between columns. Some are designed to interlock without the incorporation of columns.
It must be determined at the approval stage whether the assembly systems proposed will comply with the code, particularly in relation to storm conditions which may be encountered during the life-time of the structure.
An Engineer's certificate should be required at the approval stage certifying that they comply with the Building Standards and Code.
However that does not mean that checks should not be carried out as the Engineer's certificate will be relying on the correct method of assembly and inter-connection being used.
In complex situations it may be necessary to require the engineer or other person with sufficient specialised knowledge to make inspections and to certify that the assembly method being used is in accordance with the requirements.
An engineer or other specialist may be required to provide calculation demonstrating that at all levels of interconnection the structure will withstand normal loadings and storm loadings which may include downward forces and uplift forces.
It may be necessary to require additions to the design such as the use of slotting techniques for fixing at the floor and ceiling levels, columns to enable steel to connect between floor and roofing structure in those cases where the structure itself does not have an integrated set of columns to enable that.
Where pre-cast panels are to be used it is important that the reinforcing be adequate and properly placed. This may necessitate spot-checks being made at the fabrication plant.

Assembly - Prior to plastering




Tilt-Slab Pre-cast Concrete (Entire walls)

When the precast walls have been lifted into placed and connected




Roofing Structures

Nowadays the modern method for the construction of roofing structures, using timber, utilizes pre-fabricated timber trusses. Pre-fabrication may take place on-site or at a truss making factory. The strength of trusses is generally more satisfactory than using rafters - not that the timber is any stronger but the connection system is quite different and generally much stronger.
The timber truss system uses gang-nail plates which are nailed into the sides of timber members and chords which are butted together. As the nailing is horizontal it is inherently much stronger than skewed or vertical nailing.
Timber trusses can be designed to span any of the common dimensions normally found in residential construction with strengths able to withstand heavy snow-loadings or the strong uplift forces experienced in high wind prone areas.
A design certificate from a truss manufacturer or suitably qualified architect or civil engineer (where trusses are to be built on-site) or other appropriate specialist needs to be supplied at the approval stage. It must certify the upward and downward forces which the truss will withstand per unit length. From that can be deduced the spacing required to accommodate the risks of storms of particular intensities.
The architectural plans with a certificate, from an architect, engineer, or other consultant with specialist knowledge and expertise in the physics of roofing design for storm conditions, must give a truss and purlin plan with clear requirements as to spacings, fixings one to another and to the wall structure and the roofing to purlin nailing frequency.

On site - general and bracing

Connections to Walls

The force with which a roof structure is lifted upwards in a storm is proportional to its area and to the energy in the wind (which is proportional to the square of the wind's maximum speed). For a particular maximum wind speed the force with which a roof structure must be held down is then proportional to its area.
There are 2 excellent connecting components for connecting trusses to a timber plate at the top of timber framing or a concrete wall.

The following holding powers can be obtained wherever a truss connects to a timber bearer such as a top plate - anything else requires a special design. These 4 combinations are enough to cover what is needed for the normal range of residential dwellings
The specialist providing the roof structure design must specify the method of connection to the walls. Plywood

Unless there is a structural requirement in terms of rigidity plywood is not necessary when iron is being used with truss based structure. Plywood is also too thin a material to which to nail roofing iron.
3" x 2" purlins on the flat need to be fixed to the trusses as the structure to which the roofing iron will be attached.

Connections of Purlins to Trusses

Firstly a brief note on Purlin and Truss spacing. If the distance which a purlin spans between trusses is too much then it is much easier to snap than if it is shorter. The way to cope with this is to specify a maximum spacing between trusses. Other factors may further reduce this.
Similarly when the spacing between rows of nails along a length of roofing material become too large so that a sudden tug in the middle can cause it to tear at the nailing and rip off. The way to cope with this is to specify a maximum spacing between purlins. Other factors may further reduce this.
A roofing nail, nailed into a 2" thick purlin is optimal of it is 3" in length. (There is 1" in air between the top of the iron corrugation (or similar) and 2" into the timber.) It it is galvanized, twisted shank in nature then its holding power is 400 N. If there are 3 or 4 such nails into a purlin between 2 trusses they can hold the iron with a force of 1200 or 1600 N. It is not much sense to use a single 4" nail through a purlin as it will only hold with a force of around 500 N. Something with more holding power is needed. A Z nail will hold with 1750 N which is more than the 1600 N required. A 4" nail is needed also but for a different reason. It is needed to stop lateral movement of the purlin on the truss.
Are so many nails needed between trusses ? - The answer in a windy or hurricane prone area is Yes!


The following needs to be done at approval and construction stages

On-site




Connections of Metallic Roofing components to Purlins

This may done by one of a limited number of methods. Corrugated Iron (So called Galvanized.) needs to be nailed. The plan must specify the nailing frequency which. Some of the pre-painted baked enamel roofing materials are nailed whereas others are fitted onto clips fixed onto the purlins. Those which have a chip coating and simulate the appearance of tiles are nailed through the front of the downward facing lip.
Whichever material is used the manufacturer's instructions must be followed unless the Code or specialist's instructions over-rides them. Before the truss plan is designed the exact type of material to be used must be specified as it will affect the truss design and layout plan. The item which it must be careful to specify correctly is the exact spacing for nails of clips, to the nearest 1/16th of an inch (or nearest mm).
On-site

Ceilings


Prior to fixing of the ceiling lining


In relation to ceiling battens

Wall Linings


Prior to fixing the wall Linings


Timber framing

Steel Beams, Box Steel and other Such-like Electrical Plumbing Drainage

Prior to covering up sewage pipes in the trenches dug for them they need to be checked to determine that

Completion Inspection


Make a final inspection when the house is completed and check the following.



Summary

A building built with the code and the inspector in-mind will not only easily pass the inspections but will also stand the test of time, come rain, hail, hurricane or snow.

David L Evans Ph D

22nd November 2004


For Creativity and Quality engage Evans Construction....

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