1

Topic 7: Timber Subfloor Systems – Basic© Unitec New Zealand

Construction Systems 1

Topic introduction, overview and threshold concepts.

>>FACULTY OF TECHNOLOGY AND BUILT ENVIRONMENT

Intention of this short overview.

Students will be introduced to the fundamentals and basics of the topic area content.

Typical elements used in Timber sub floors will be identified using photos , images and drawings .

Words and terms used to describe and identify elements will be explained .

Terms used in the design of the major elements such as Spans and Loaded Dimensions will be introduced leading to future detailed discussion in breakouts.

Design approaches to simple layouts will be outlined with terminology defined and explained for future discussion in tutorial breakouts.

Additional non structural functional requirements of sub floor framing identified , implications and prevention of possible problems.

Additional requirements and terms that relate to residential timber mid floor framing

Definition: Subfloor refers to the bottom-most structural floor underneath the decorative or "finished" floor.

© Unitec New Zealand

Timber Subfloor

Sub floor elements shown in context with concrete slab and foundation walls which often provide some form of support.

© Unitec New Zealand

Timber Subfloor

It is also referred to as a suspended timber floor system as the floor is built up off the ground creating a ventilated space in between.

Timber Subfloor – typical sequence of construction

Typical sequence of construction. Usually a concrete slab on ground will have been laid already. These elements will be the focus of lecture topic 10 in week 4 .

Every building needs a site .

Excavations carried out and then strip footings and foundations walls for concrete slab provided.

Timber Subfloor – typical sequence of construction

Elements of concrete slab in place. This building also had some masonry piers

Concrete and masonry elements in context with the site.

Timber Subfloor – typical sequence of construction

Circular concrete footings poured to required depth of embedment

Footings in the ground.

Timber Subfloor – typical sequence of construction

Treated timber piles are embedded in the footings.

The distance between bearer supports is called the BEARER SPAN.

This is the same as the PILE SPACING.

Treated timber bearers then span between the supporting piles. Direction, layout and sizes will be decided by the designer using NZS 3604 2011.

Timber Subfloor – typical sequence of construction

The sub floor joists will span onto the bearers but sometimes onto other elements such as stringers and plates , eg where masonry piers are present.

Stringers are usually fixed to slab edges or walls.

Joists can also span onto timber plates on a DPC over masonry piers .

Treated timber joists span onto the bearers and sometimes onto elements called Stringers.

Timber Subfloor – typical sequence of construction

Finished assembly of elements of a residential timber sub floor framing proposal .Yellow piles are where designer identified the need for extra piles to deal with special loads from above.

Timber Subfloor – typical sequence of construction

Design of framing for decks follows practically the same design procedure but installation at later construction stage.

Finished sub floor framing in overall house context shown on right and includes later framing for decks.

Timber Subfloor – What is a LOAD ?

A structural load is basically weight or MASS but it takes into account the effects of gravity

MASS is measured in Kgs but LOADS are usually calculated using a unit called the Newton. Don’t worry , structural engineers usually get paid to do all the hard calculations

Timber Subfloor – What is a LOAD ?

NZS 3604 has tried to make things easier for designers . They employ a method called the LOADED DIMENSION.

Unit of mass is a KG A LOAD is a FORCE. The unit of both is the NEWTON

Timber Subfloor – What is a LOADED DIMENSION ?

When starting to study NZS 3604 it may help to think of the span distances and measurements as being similar to, or as representing weights and forces.

If each man represents a metre ( 1m ) , what are the loaded dimensions of the men on the bottom row ?1. 2. 3.

Timber Subfloor – What is a LOADED DIMENSION ?

1. 2. 3.

Doing this takes practice and so does trying to identify the loaded dimension so don’t be too worried if you don’t get it first time .

Hang in there , look at NZS 3604 and ask your tutor to go over the things you are not sure of .

Timber Subfloor – What is meant by SPAN?

Akashi Kaikyō Bridge- Longest main central span since 1998. Span is 1991 metres

Structurally- effective span is “ The centre to centre distance between the supports of a beam, girder , or other structural member.

Timber Subfloor – What is meant by SPAN?

Lets get back to basics or at least the residential scale

Diagrams from NZS 3604:2011

If you can’t quite understand whats happening in the sub- floor structure try sketching it out and add notes . Ask if still not sure what’s happening.

Timber Subfloor – What is a CANTILEVER?

Member 3 at right is a CANTILEVER.

The support of the element above is at one end only.

A CANTILEVER is fixed or supported at one end.

Its basically a diving board !!!

>>FACULTY OF TECHNOLOGY AND BUILT ENVIRONMENT

© Unitec New Zealand

19

END

“ Next session we will be studying

Mid Floor systems “

“May the Loaded Dimension be with you “