With so many structural framework options available to lay your deck boards on, the properties of these materials can be confusing. That is why we are going to take you through the pros and cons of softwood and composite frameworks so that you can make a well-informed confident decision, no matter what material you go for.
What framework material should I choose?
We recommend that all elevated timber structures should use load-bearing timber. However, if the material is used at ground level and is subject to standing water and high moisture for long periods, then the material will endure a shorter lifespan.
As a result of poorly constructed ground level decks in the UK in the past, the opportunity arose for the implementation of recycled plastic compressed with bonding agents which formed joist sized beams. This, in theory, sounds ideal, however, several things must be taken into consideration when opting to use composite joists as a structural framework.
This in theory sounds ideal however, several things need to be taken into consideration when considering composite joists as a structural framework. By its nature plastic is susceptible to changes in temperature and will expand and contract during hot and cold weather. If the composite framework is not adequately braced out and securely screwed or bolted together, this movement will affect the stability of the overall structure and will be noticeable on your deck boards. In turn, this material will not have the same unsupported span strength that you would receive with an equal-sized timber beam. Meaning that more support posts will be required and your deck may be susceptible to a shorter lifespan.
In addition to this, when opting for a composite framework, your choice of joist size and length is much more limited compared to timber and the cost per metre is roughly three times more than a timber equivalent.
Structural and kiln-dried C16/24 graded softwood which is preservative treated and machine regularised and is also graded for reduced knot content to improve the overall strength of the timber joist is recommended. Using a softwood material is the most cost-effective and environmentally-friendly product for fashioning decking structures.
Where can I use composite and timber frameworks?
The most common area for the implementation of composite frameworks is in wet areas or flat surfaces like roof terraces, patios and low-level balconies due to their rot-resistant properties.
If you would prefer to use timber joists at ground level, where air circulation is reduced compared to exposed elevated structures, then you must follow the next steps to ensure your framework will last for over 15 years.
You must ensure that all of the cut ends of your timber are properly treated with an end-grain preservative at the time of construction, as this part is most susceptible to moisture and insect ingress. You can purchase this treatment here.
There must be adequate ground clearance under the bottom of the joist, to allow water to run and drain away so that it is not absorbed by the timber.
Lay a heavy-duty weed control fabric on the ground. This will allow water to drain through and prevent vegetational growth. You could weigh this down with shingle. Purchase your weed control fabric here.
Ensure that your support posts are either Class 4 treated and measure 100mm x 100mm or are larger. Again, these ends must be treated and the top of the post should be angled slightly to encourage water to run off. These posts must be concreted into the ground.
To prolong the life of your softwood frame, you should staple a 100mm wide roll of DPC on top of the frame. As well as creasing down each side of the joist you have covered with a screwdriver or a piece of wood. Encouraging water to run off. When you screw down your deck boards, the recommended 5mm gaps between each board will be covered and will prevent water from migrating between the deck board and the joist, where most softwood frameworks start to deteriorate.
In conclusion, the longer your timber framework stays dry, the longer it will last. Alternatively, you can use concrete slabs or blocks as well as recycled composite 100mm x 100mm posts providing they are short, to avoid flexing.
It is important to remember that no matter how durable and high quality your deck boards are, their lifespan will be solely reliant on a stable and robust structural framework to support them.
To discuss your decking framework, call our Sales team on 0118 373 2211 for expert advice!
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