Structurally Engineered   
Floor Joists & Floor Decking

Engineering Requirements   Value for Money   Heat & Sound    Decking & Access    Wet Rooms    Rot & Infestation    Squeaking Floors    Solutions  

Whether you build using a timber frame structure or any other form of construction, the chances are that you will need floor joists for one or more levels of your building. 

Engineering requirements
And if you do, then it is more than likely that these will need to be properly engineered and full engineering calculations provided for your building control authority.

True, span tables will provide you with a 'rule-of-thumb' means of determining what joist size you should use, but reliance on such joist span tables may not be acceptable to your building inspectors.  

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Value for Money
Furthermore, because they are only 'rule of thumb' they may not give you either the best solution, or the best value-for-money,

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Heat & Sound
There are also other considerations to be taken into account.  Thermal insulation, for example, not to mention sound transference.  Both are sensible considerations in a single dwelling house, but in, say, a block of flats, or any other structure that is for multiple occupation / use, then they are absolutely crucial to the design of your structure.  

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Services
Then there are the electrical, plumbing, water, telephone, gas, heating, mechanical and other services to consider.  Almost certainly they will need to pass through the area between ceiling and floor surface at some point - possibly many.  That is to say, they will need to occupy some of the same space as your timber floor-joists.  This introduces yet further floor-joist engineering considerations - can space be 'cut' in or through the joists?   If so, where and how can they be cut?  If not, how else can they be accommodated?  

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Floor Decking and Access 'traps'
In making provision for these services, don't overlook the need to gain access to them between joists for their own servicing and/or replacement.  Can they be accessed to repair a leaking joint, for instance?  Or to overcome some vibration?  Perhaps even to connect and install an additional piece of equipment, e.g. a 'bidet' in the bathroom?  Somehow, and somewhere, access points, or 'traps', will need to be provided for such work.  But these must be done without adversely affecting the structural integrity of the floor itself.  You may also want to think about these provisions in relation to your finished floor surfaces.  How, for example, will you be able to lift out the access traps?  Will identical 'cuts' need to be made in the finished floor surface?  How will they both be supported? and so on.

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'Wet Room' Floors
In areas such as bathrooms and utility rooms you may need to provide waterproof protection between the joists and subsequent floor decking to prevent water getting through and damaging the joists - and any services that occupy the same space.  This will be especially true if you decide to opt for a tiled floor surface in such areas.

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Rot and Infestation
If joist-ends are built into masonry walls, then these should be properly treated to avoid rot, fungus or other infestation.  If the joists are of impregnated timber and are cut for any reason, then the cut end must also be treated with the same material as the impregnation.  

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Squeaking Floors
If your joists are not correctly sized, if they have not properly provided for subsequent service 'runs', if access traps have only been an afterthought, if the moisture content of the floor joists and other materials was not controlled during construction, if subsequent drying out affects the jointing and junctions between joists and the other components, if water vapour or other moisture is able to get through to your joists ... just to identify some of the more important issues, then you could end up with ''squeaking floors'.  And we all know how mind bendingly irritating that can be.

In fact it has become more of a problem in modern houses for three reasons.  First, the greater use of central heating, particularly since the 1960's.  This dries out and 'shrinks' timbers, causing them to pull at their fixings and things that are fixed to them, like floor boards.  Second, the greater use of sheet boards, like plywood, block-board, and chipboard, especially where these are not properly fixed, e.g. by gluing and screwing.  Third, by insufficient attention being paid to access 'traps' so that these do not fit, or 'seat', correctly with other components..       . 

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Solutions
'Horses for Courses', is not a bad rule to follow here.  Depending on the type of structure you have opted for, then your risk may be greater or lesser for each and every issue identified above.  We hope it will come as no surprise, therefore, that we recommend that full and proper consideration should be given to the both the type of floor joists used and the engineering structure of the 'joist frame'.  Additionally, it is advisable to try and control the moisture content of all materials used both before, during and after their installation. 

It is one reason why we advocate that, when we are engaged to design, manufacture and erect a timber-frame structure, this should be for the delivery of a 'wind, watertight and secure' building.

Typical materials supplied and used  by us in this process are:-

• Stress graded softwood carcassing timbers, properly strutted and braced within the joist frame
  

• Specially graded and vacuum treated softwood to provide solid joists with circa 14% moisture content (i.e. the same level as a centrally heated house in the UK).
  

• Composite 'I' beam joists, having top and bottom softwood cords and a moisture stable flange of ply, kerto, laminate, or particle board.  Greater spans as well as higher moister stability can be achieved with these materials.  However, great care has to be taken with the size and positioning of service holes to avoid weakening the beams.
  

• Engineered 'web' joists, or 'trussed' joists', having softwood top and bottom cords fixed together with metal webs or struts.  These allow almost unlimited access for service runs..
  

• OSB panel sub deck.  These sheets, or panels, are fixed to the top surface of the joistings, ready to receive the finished floor on top.
  

• Weather protected particle board decking.  Fixed directly to the top surface of the joist-frame, these have a 'peel-off' membrane that protects the floor surface from rain, snow, frost, and wear and tear during construction.  They may be used as either a sub floor, or the finished surface below carpet or other sheet flooring.     

If you have a particular requirement, problem, or just general query, please Contact Us, without cost or obligation to discuss the right options for you.

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Engineering Requirements    Value for Money    Heat & Sound    Decking & Access    Wet Rooms    Rot & Infestation    Squeaking Floors   Solutions