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Rotted deck frame - use the right timber in the right way

Given the popularity of decks and DIYing them here on Workshop I thought it's important to show the perils of not installing them correctly.

In all my responses to people (and obviously the decks I build) I advise to use;

H3 timber with a 250mm clearance between it and the ground because it can't be in constant contact with moisture
H4/H5 timber for posts/stumps, the outer frame and anywhere else there isn't sufficient clearance causing the timber to be in constant contact with sand, concrete, etc and ultimately moisture.

Below are the results of not following this advice. Someone installed this deck with no clearance - H3 sitting on the sand below. This deck was installed about 6-7 years ago and is beyond repair.

Decking boards are sinking. I can pull them up with just my fingers. Pressing on the rotting frame causes it to crumble away. It's become very dangerous.

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Comments

MitchellMc

Hi @ProjectPete,

Many thanks for sharing this example with the community. Did they use H3 in this situation because there wasn't enough clearance to fit the suitable H4 sizes? I've noted that in many of the low-level deck builds there just isn't enough space to fit H4 joists/bearers without adjusting the ground height first. After contacting some manufacturers it appears 90 x 45mm H4 just isn't something readily available.

What will be your solution to this issue, to dig down, raise the deck or was there actually room to fit the adequate H4 timbers already?

Mitchell

ProjectPete

https://www.workshop.bunnings.com.au/discussion/comment/9064#Comment_9064

It's a case of making the room to be honest @MitchellMc. It adds labour and cost to do so, but you need to dig that sand away to create the 250mm clearance for H3, or at least make enough room for H4. You could rip lengths of 200x50 H4 sleepers to size. These are readily available.

If you're not going to create the right space and use the right timber, don't install a deck. The deck cost my customers about $11,000 and it's going to cost more than that to remove existing, dispose of it, create the clearance and install a new deck.

Noyade

https://www.workshop.bunnings.com.au/discussion/comment/66784#Comment_66784

Do termites still attack H3/4/5 wood?

(I never knew there was a H5).

ProjectPete

https://www.workshop.bunnings.com.au/discussion/comment/96181#Comment_96181

@Noyade H3/4/5 are all treated for termites.

H4/5 gives you the treatment against continual contact with ground/moisture and H5 can actually be submersed in fresh water.

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/96181#Comment_96181

Hi @Noyade, @ProjectPete

For the benefit of others that might come across this discussion, I thought I would include the 6 general grades of treated pine.

H1 which is suitable for internal use. It offers protection from Lyctid borer. Its common uses are in framing, furniture and interior joinery.

H2 which is suitable for internal use with occasional slight wetting. It offers protection from borers and termites. Its common uses are in framing.

H3 which is suitable for exterior above ground use where it receives moderate moisture. It offers protection from moderate decay, borers and termites. Its common uses are in facia, bargeboards, window joinery and framing.

H4 which is suitable for exterior on/inground use where it receives moderate wetting. It offers protection from severe decay, borers and termites. Its common uses are in fence/decking posts and landscaping.

H5 which is suitable for exterior on/inground use where it is in constant contact with fresh water. It offers protection from severe decay, borers and termites. Its common uses are in retaining walls, piling, house stumps and building poles.

H6 which is suitable for prolonged immersion in seawater. It offers protection from marine wood borers and extreme decay. Its common uses are in boat hulls, marine piles and jetty cross bracing.

These treatments are only effective on un-cut lengths of timber and the internal timber is not treated to the same degree. Any cut lengths must be resealed on their ends with a product similar to TWA Woodcare 300g Ecoseal Tanalised Timber Treatment to retain their H rating and characteristics.

Mitchell

Noyade

https://www.workshop.bunnings.com.au/discussion/comment/114682#Comment_114682

Thanks guys.

Dunno why, but I always thought the "H" rating represented weather resistance only.

Cheers.

Graeme.

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