Pitched Roofs – to Cut or to Truss

There are two basic methods of pitched roof construction;

1. A ‘cut roof‘ – this is the traditional method of cutting the timber on site and building up the roof using rafters, ridge boards, joists and purlins etc – the exact details being determined by the size of roof, size of timbers etc.
2. A ‘truss roof‘ – using factory made trusses which are delivered to site complete and just erected.

Current day building regulations require detailed calculation of the stresses, timber size etc used in roof construction, so factory made trusses are becoming the standard practice where all this can be worked out on a computer.

A cut roof

In simple terms this type of roof consists of rafters and joists. The joists prevent the outward spread of the rafters/walls, and conveniently give support for the ceiling below.

The size of rafter timbers will depend upon their length from the wall plate to the ridge, the type of roof covering and whether purlins are incorporated in the roof. It is more economical to keep the cross section of the rafters down, however where an open roof space is needed, larger rafters will be necessary. Typical rafter spacing is 400mm (16 inches), closer spacing will allow small section rafters and batten, that are fixed to the rafters to locate/fix the slates or tiles, to be used. The wider the gap between the rafters, the thicker the rafter and lath timbers need to be.

Rafters are nailed to a wall plate at the top of each supporting walls, these are normally 100x75mm (4×3 inches) timber embedded on cement mortar on top of the inner skin of a cavity wall, or the inner part of a solid wall. The wall plate timbers along the top of each wall should be joined with a half lap joint where they meet.

Each rafter has a small triangular section (referred to as ‘birdsmouth joints’) cut out of them to allow them to fit neatly over the wall plate. The top of the rafter is cut at an angle and nailed to the ridge board, typically 175mmx32mm (7×21/2 inch) mounted vertically.

Purlins, and the associated struts, are used to give some additional support for the rafters. The purlins run at right angles to the rafters, the associated struts are positioned under every forth (or so) rafter to attach to a joist above a supporting wall below.

Hangers, in conjunction with a longitudinal binder running at right angles to the joists, are used to help hold the ceiling up. Each hanger is nailed between the every fourth (or so) rafters and the joist below. The larger the joists size, the less likely there will be a need for hangers.

Collars, ridge collars and/or collars further down the rafters, are sometimes used to provide additional binding between the rafters on both sides of the roof. Where used, they are usually fixed to an occasional pair of rafters along the roof.

No part of a timber roof should ever be cut, modified, remove or the covering of the roof changed (i.e. replacing a slate roof covering by a concrete tile covering) without consulting a structural engineer.

A truss roof

A truss roof is made up of a number of factory made frames (or trusses) each of which which combine the joist, rafter and struts. The illustration to the right shows a typical truss for a simple Duo ridge roof.

Each modern roof truss is designed and made for a particular position in the roof structure and is made up of butt jointed timber lengths typically nailed together using plate fastenings – no type of timber joint being used. Historically truss timbers have been bolted together, or mortise and tenoned and then pegged.

As each truss is designed to form part of the complete roof structure, they should never be cut, modified or their use changed (i.e. replacing a slate roof covering by a concrete tile covering) without consulting a structural engineer.

Now that you know a little more, you can discuss roofing options with your North Carolina roofing contractor and determine which roofing system is best for you.

Article Source: http://diydata.com/general_building/roof_construction/roof_construction.php

So if you are looking for a professional North Carolina roofing contractor, then please call us today at 1-888-DRY-CLUB or complete our online request form.

Metal Roofing May Provide Valued Choice

Have you ever driven through the Southport, NC neighborhood and remarked how different and unique a particular metal roof looked? You probably thought a metal roof was way too expensive for your budget so you never even considered one for your North Carolina home. Lots of people believe the same way you do, not realizing that residential metal roofing prices is available at affordable costs. In fact, many experts will tell you that metal roof products are very good long-term investments.

Now a Good Looking Top

Since these roofs can be designed to look like other types, you will not be able to tell from on the ground that a simulated cedar-shake metal roof was not the real one. Lightweight steel roofs can be painted through a special process where real earth-tone granules are embedded in the final paint coat that then is covered with a high-protective clear coating.

Safety Sells

There are quite a few advantages using a this type of roof. For one, they do not burn! Aside from the obvious benefit from not being able to burn, a home topped by a metal roof may result in significant savings when it comes to insurance costs.

Energy Savings

During the summer, a metal roof causes less attic heat than traditional roofs while retaining a greater amount of warmth during the winter. This can be seen as a significant reduction or retention – as much as 34 percent in warm climates. The savings in air conditioning alone can warrant purchasing a metal roof.

Easy Installation

For homeowners thinking of making a switch to lightweight steel roofs, installation over old shingles is possible eliminating the need for any costly tear off. Metal roofing is manufactured in large sheets making it easy to install by experienced roofers.

Copper is Cool

Roofs made from copper not only provide all the benefits mentioned concerning steel roofs, but produce an aesthetically pleasing weathered green patina over time. The great drawback choosing copper is that it is very expensive and can price out as much as $1,100 per square.