Wee deck project

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Willuknight

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#213875 16-Apr-2017 17:45

So I'm going to build a small extension to my deck to house a spa pool.

I've never built a deck before, but it seems pretty self explanatory, I've looked up all the how to guides to base my measurements on, just figured I'd ask if someone can give my plans a once over as well?

Also I can't seem to find any information about the thickness and type of wood I should be using as like a fascia, i know you're supposed to cover up the cut decking with trim, but I can't find any info about what that usually would consist of.

The entire structure consists of 150x50mm h3 wood, with one pile and on the furthermost end it will be bolted to concrete.

More here:

https://imgur.com/a/4y5Ih

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#1765115 16-Apr-2017 18:51

Very impressive drawings.

All we did to finish the edging on our desk was flip the desking timber so the smooth side was up and just nailed that vertically on the edge of the deck. I'm rubbish at measuring so just always gave myself a good 50-odd-mm extra and then just laid a chalk line and then scooted along that with the skilsaw to get it all even. Probably a bit wasteful but I just find it soooo much easier.

What's the story with a spa pool? Do you have to fence it? Or is the hard top cover sufficient?

mdf

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#1765116 16-Apr-2017 18:58

Your sketchup skills are better than mine!

I am not a builder, but deck #4 is currently in the planning stage (see this post for number 3).

The facing board will depend on what are you using for decking. If you're using something nice, I would just use some decking boards to match. Looks kinda cr@ppy to use treated pine to face something nice (having done just that on deck #1).

Usual issues are bearer and joist spacing (can't see the framing on the images you uploaded but happy to have a look if you post those too). Make sure you pack out the stringer to let the water flow/give the stringer some breathing space. For the steps, I'd be inclined to rotate thee decking boards 90 degrees. The orthodox view is you're less likely to slip across boards than along them. Make sure you get at least H3.2 (probably H4 would be better for a wet area like around a spa).

I also have no idea about rules and regulations regarding either supporting a spa, or around fencing/covering something at deck level.

Bung

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#1765119 16-Apr-2017 19:24

Willuknight:
So I'm going to build a small extension to my deck to house a spa pool.

I've never built a deck before, but it seems pretty self explanatory, I've looked up all the how to guides to base my measurements on, just figured I'd ask if someone can give my plans a once over as well?

The weight of a spa pool could be a lot heavier than the usual deck structure is designed for. This earlier post refers. http://www.geekzone.co.nz/forums.asp?forumid=141&topicid=121071

mattwnz

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#1765132 16-Apr-2017 20:23

I would contact your council as to whether that is allowed, as you have an access route going next to a spa pool. I believe the laws regarding fencing spa pools in general have been relaxed recently, and in some case you may only need a lockable cover. Although not sure if that applies to inground spas. Personally I don't agree with this change, as I think all spas should be fenced with a self locking gate, like pools, as they are potentially just as dangerous with young children, and people forget to put on covers and lock them .. I would also doubt you could have a point load of a pile to hold up the spa, you should read the installation instructions to see how it should be supported.

In regards to the design, it looks odd to have the decking direction on the stairs in a different direction to the main deck. In terms of a fascia, just a board nailed to the side of the piles, which will also form an edge for the decking. Something like a 45 mm thick fascia will produce a nice edge, although more expensive to do.

But contact your council, as you don't want to build something that may have needed a consent anyway, as it could reduce the value of your property and could affect insurance.

Jase2985

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#1765133 16-Apr-2017 20:29

a basic 4 person spa will come in at about 1400kg's full, and then add 4 people at an average weight of say 75kgs and thats close to 1700kgs over 4msq. so 425kg per m2.

Willuknight

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#1765138 16-Apr-2017 20:59

Hi guys,

I can see im going to need to upload a better sketchup drawing. The bit i'm adding is only the steps around the spa. The spa is going to rest on a gravel / sand base -i'm digging that out at the moment.

Jase2985

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#1765176 16-Apr-2017 21:23

or just describe what your doing a little better in the first post :)

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nickb800

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#1765177 16-Apr-2017 21:26

Yeah I'd agree that you should run the boards on the steps the other way - perpendicular to the direction of travel. Regardless of whether you have a tread facing upwards or not, the groove between boards will provides some skid resistance in wet or frosty conditions.

I can't tell how you are going to fix things, but I would suggest

- Weight is well taken care of

- Think about twisting, particularly around the middle of the steps. This could be mitigated by fixing both the upper and lower joists into the house and the pile, and with 2x8" blocking inbetween both upper and lower joists.

Generally speaking, looks solid

Willuknight

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#1765186 16-Apr-2017 23:06

I've finished editing the sketchup and have uploaded the files to imgur: https://imgur.com/a/4y5Ih

So basically I'm building the bit to the right to go around the deck, so just the white top deck parts are new construction, everything else is existing.

The spa will sit on the ground - I'm digging about 40cm down, and going to fill that with gravel and then compress, before leveling with sand.

I'm dividing the construction into two parts. The back step part will go in first. The higher platform will go in later.

chevrolux>

Spa's legally require fencing or a locked cover AFAIK. My cover will be lockable.

mdf>

Gotta start somewhere, I'm entirely self taught. Best thing to do is find a model close to what you want and then start picking it a apart. I've posted the framing in the imgur album, linked above.

Planning for H3.2 but will ask the guys at the yard about exposure to water from spa.

Oh man, I just looked at your deck 3 - super sexy. I bought some galvanized square head screws, do you reckon those or nails would be good for attaching the decking? And what sort of tools do I need in terms of putting bolts through the lumber? Will a normal drill handle it? Also (sorry for all the questions) I have NO idea about wood - was just going to ask the landscaping place. Any suggestions for a small budget?

Mattwnz>

So this side of my deck is actually my usless side. The sketchup is slightly inaccurate because i just grabbed the closest house with a porch I found, but basically my main rear entrance is to the right of the deck - opposite end to the spa. There's also a 'front' set of steps which go to the garden. Before this goes in, there is no access to the 'right' side of the house as that end of the deck was closed off. Also my main deck is lengthwise, again I just didn't change the sketchup model.

Nick>

Yeah I was doing the decking the same direction as the rest of the house, (ignore the sketchup, it's wrong). Interesting point about the increased grip, but I guess if slipperyness is a problem i can add antislip paint. Can you tell me more about what you mean about the other stuff you mentioned? I'm a complete novice and don't really understand the problem or the fix. Is twisting the deck not being properly supported?

nickb800

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#1765187 16-Apr-2017 23:16

Bear in mind that antislip paint doesn't work in frost conditions (not sure what part of the country you're in) as moisture fills the undulations of the antislip surface before freezing

Think of it this way - if you were standing on the stairs, in between the bottom and middle pile, or top and middle pile, and you stomped your feet left to right, what part of the structure would be resisting that force and holding the deck steady?

Looking at your updated plan, I think you would be fine in that respect, provided that the steps are bolted into the piles of the house. This may require a bit of packing if there is a gap between the deck and cladding of your foundations, and/or between the cladding and house piles. Alternatively, add another pair of piles right up close to the house.

For timber treatment you want H4 for the piles, H3.2 for everything else

Willuknight

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#1765212 16-Apr-2017 23:22

Yeah I'm going to pack the stringer. Does the pile have to be H4 if it's not coming in contact with the dirt ? Just wondering. I want to use concrete anchor brackets.

I imagine we'd be fine as we've never had frost on the rest of our deck for the year I've lived here, it's never been slippery either. Christchurch doesn't really get big frosts on covered parts of the house.

Bung

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#1765223 17-Apr-2017 04:33

Piles in the ground need to be H5 now. Above ground you'd probably find the size timber is more readily available as H4 than anything less. The cost should be much different.

Disrespective

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#1765242 17-Apr-2017 09:49

OK, so i'll admit i've not read all the posts verbatim, but you need to understand that NZS3604 is what you need to look at to find out the right sizes of timber members.

Some basics that you should consider are:

- Use 19-21mm thick decking timber with joists no more than 450mm apart.
- Use 32mm thick decking with joists no more than 600mm apart.
- Don't forget to allow blocking to fix both sides of the decking boards along the ends.
- Make sure any attached stringers have min. 12mm clear gap from the house structure. This also means you need to look at the bolt build up of metal and EPDM washers to ensure no water ingress into the house structure.
- All piles have to be H5 treated. All timber touching the ground needs to be H4. Timber within (I think) 300mm of the ground needs to be H3.2. Check 3604 for this.
- Any falls of over 1m need a compliant handrail.
- Consider ease of installation/removal of the spa pool. Don't assume 15mm each side will be enough if you aren't confident.
- What decking timber are you going to use? Don't forget to pre-prime the cut ends of the boards before you put them down so you don't have them split.

Your spans are pretty small so 140x45 joists would probably be OK. Bearers should be OK at 90x90 or maybe 140x90 (2 140x45's nailed together). You'd need to check your spans to make sure this is OK. This is in 3604 or probably online with the deck guides.

Source: Am an architect who just built his own deck.

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Wilko

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#1765276 17-Apr-2017 12:31

The suggestions so far are very good, but a couple of points:

If the deck projects more than 2 metres from the house, you must allow for subfloor bracing by either anchor piles or braced piles. The bracing calculations can ignore wind loading and are calculated at half the value of earthquake loading. For reference, see NZS 3604:2011 section 7.4.

The grooved face of decking timber is designed to face down to the underside of the deck. This is to allow ventilation to the joist/decking junction. Having the grooved face upwards actually makes the deck more slippery, especially when mould and dirt accumulate. The deck, if the main access to the house, must have a slip resistance of not less than 0.4 when wet (but who is going to check that?).

Calculations for loading of a deck must be 2 kPa rather than 1.5 kPa for floors to houses.

neb

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#1765314 17-Apr-2017 14:08

Willuknight:
So I'm going to build a small extension to my deck to house a spa pool.

I've never built a deck before,

So just a general comment, what's your building knowledge and skills like? This seems rather more complex than just concreting in some piles and laying a deck on them, which means you'd need at least some experience and specialised knowledge on how to do it. You really need to use the correct tool for the job for something like this, and for this sort of job I'd say the correct tool to apply is a builder. It looks like the sort of thing that a standard builder would do as a side-job over a weekend or two, which could save you a lot of headaches in terms of getting all the details right.

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