Porch floor frame plan help

OK - I'm part way through renovating my first house (circa 1920's Cal Bungalow), of which I am doing most of the work myself, bar electrical and plumbing. For the most par it has been fun and a great learning experience.

The time has come to replace the floor and sub floor on the front porch. I have attached an image of the dimensions below. This is the first time I have had to frame up a floor and am looking forward to the challenge. It will be the small scale warm up to a bigger deck project out the back later.

The area is completely undercover and the floor will be 80x19 tongue and groove WA Karri, with the floor 'pitched' at about 5-10 degrees to deal with any wind blown rain that might make it's way in. I am struggling a little for depth, but think I should be able to get the top of the deck 300mm above the ground with a little bit of excavation, possibly up to about 100mm more at the 'fat' end (see diagram). The original deck had the bearers sitting directly in the soil on one side and on <100mm stumps on the other - I'm surprised that they lasted as long as they did!

Now, I have bought Alan Stains Decks & Pergolas and it is a great little book, however I am having a bit of trouble with the span tables in trying to work out how many bearers and joist I will need and what dimensions.

At this stage, I am thinking 90x90mm stumps (in stirrups?). What size bearer will I need to make a single 1560mm span and how many of these will I need (spacing?) given the orientation shown on the diagram? Or would I need a 3rd stump in the middle?

Likewise, I am wondering what dimension and type of timber I will need to use for the joists? Because of my clearance issues, I guess joist hangers are the way to go to save some digging. So am I correct in assuming these to be single span of whatever spacing is determined as above.

Any help from those more learned would be much appreciated!

Why not use concrete stumps with reo out the centre? See the Cope website for pictures.

I don't have the tables with me but a good guide to give you an idea of sizing and spacing is to look at how the floor for the rest of teh house has been done.

However, if you want to use joist hangers that is probably a whole different set of span tables. You could also consider soemthing like Hyspan manufactured timbers that may get the depth down a bit but possibley a bit more expensive? They also have software on the web to do the span calcs for you.

Why mess around with stirrups?
As clearance is an issue you could set the bearers up higher so the tops of the bearers are at the same level as the tops of the joists.
In such case the joists will need to snugly fit between the bearers

Quote:

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Originally Posted by echnidna

As clearance is an issue you could set the bearers up higher so the tops of the bearers are at the same level as the tops of the joists.
In such case the joists will need to snugly fit between the bearers

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Yup - that's what I plan to do using joist hangers.

I think I have made some progress with the span tables. The thing that still has me a bit stumped (no pun intended) is how using joist hangers effects the joist span. Am I correct in assuming that when using hangers, the joist is a single span?

With respect to stumps, I had considered concrete but don't know how short you can get them. Given that the top of the stump will be no more than 100-200mm above the ground, they probably only need to be about 800 in total? I was thinking about timber for ease of use - say something like red gum or Ironbark if I could get my hands on it. Any thoughts?

Now back to my original question - how many bearers and what size do you think I need and what spacing? (which will determine the joist timber dimensions as soon as I can find out the the deal with hangers)

I reckon that 5 bearers spaced at about 1500mm with the appropriate timber for the span (don't have the tables here at work) sounds about right.

Damn, that means 10 holes...I hate diggin holes...

Ive had concrete stumps at 700mm, they are very cheap ... but for such a small area it may be easier to use timber?

Yep - single span between bearers ... i.e. not considered continuous span.

Don't have the span tables here ... but appropriate timber size is the key to the spacing and span. 1500 or 1800 is probably fairly normal but it really depends on what timber strength and size you choose.

Actually, looking at the tables on the TRADAC site, and assuming that by using joist hangers you make the span between bearers a single span (which could be well off the mark), it looks I would need:

Bearers: 1/140 x 35 or 190 x 45 - F7 treated pine

5 bearers spaced at approx 1522mm

Joists: 120 x 45 - F7 treated pine

4 joists @ 450 centres.

What do we reckon out there?

Ben

Quote:

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Originally Posted by Ben (TM)

Yup - that's what I plan to do using joist hangers.

I think I have made some progress with the span tables. The thing that still has me a bit stumped (no pun intended) is how using joist hangers effects the joist span. Am I correct in assuming that when using hangers, the joist is a single span?

Yes - it is the length of the joist not the manner of fixing the ends. Technically skew nails are good enough 2 each end, 1 on each side but joist hangers or hoop iron supports is a good practice

With respect to stumps, I had considered concrete but don't know how short you can get them. Given that the top of the stump will be no more than 100-200mm above the ground, they probably only need to be about 800 in total? I was thinking about timber for ease of use - say something like red gum or Ironbark if I could get my hands on it. Any thoughts?

From memory concrete starts at about 450mm long.
If you prefer timber the most durable is native cypress

Now back to my original question - how many bearers and what size do you think I need and what spacing? (which will determine the joist timber dimensions as soon as I can find out the the deal with hangers)

I reckon that 5 bearers spaced at about 1500mm with the appropriate timber for the span (don't have the tables here at work) sounds about right.

Sounds about right but refer to the tables

Damn, that means 10 holes...I hate diggin holes...

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So Do I

Thanks Bob. I noticed you are from Timboon. I spent the first 8 years of my life near Simpson, just down the road. I've not been back since, but wouldn't mind getting back there to see what became of the family farm.

Cheers
Ben

Hi Ben,

I'm in the middle of building a deck out the back of a 1920's Federation in Perth that had the same height restrictions as your front porch (330mm from ground level).

I'm no builder but went through the same process you are going through. What I have done is this:

Galvanised 90x90x300mm stirrups in concrete connected directly to 2/120*45 CCA pine beams with the stirrups at 1500mm spacings and the beams are 1000mm apart. The 120*45 lengths are nailed together from both sides with galvanised 75mm timberlock nails. The stirrups are connected the the beams by 2 galvanised bolts.

I topped the beams with that black plastic decking weather strip stuff to reduce the likelyhood of water seeping in between the beams.

The joists are 90*45 CCA Pine and spaced at 400mm centres, I used Pyrda 3 way brackets to fix the joists to the beams.

Decking is 19x90mm Batu.

This leaves 100mm of space beneath the beam and the ground.

I fixed the stirrups to the beams, lay the beams with the stirrups up so I could mark out where to dig the holes. Dug the holes and suspended the beams over the holes to the height required using bricks and wedges with the stirrups down awaiting concrete. This allowed me to ensure the deck was as level.

It exceeds minimum span specs and it's as solid as a rock, no bounce whatsoever.


Good luck!:)

PS
I'd suggest your 5-10% drop sounds excessive, 1-2% would probably do it unless you need the wheelchair access?

Thanks for your input Flats. The stirrups sound like they would be easy to set up in the manner that you did it. Just one thing, you mentioned that:

"pine beams with the stirrups at 1500mm spacings and the beams are 1000mm apart"

Can I just clarify that your bearers (beams) are 1000mm long and you have one of these every 1500mm?

Yeah 10% is excessive, but I reckon 5 would be required on a solid timber floor. I'm not too keen having water sitting around on it at all - that's why the last one was rotten!

Quote:

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Originally Posted by Ben (TM)

Thanks for your input Flats. The stirrups sound like they would be easy to set up in the manner that you did it. Just one thing, you mentioned that:

"pine beams with the stirrups at 1500mm spacings and the beams are 1000mm apart"

Can I just clarify that your bearers (beams) are 1000mm long and you have one of these every 1500mm?

Yeah 10% is excessive, but I reckon 5 would be required on a solid timber floor. I'm not too keen having water sitting around on it at all - that's why the last one was rotten!

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Hi again,

No, my bearers were 7.2m long, each bearer was 1000mm from the other bearer (ie the joists were spanning 1000mm). I had a cantilever at each end of 400mm and 5 posts (stirrups) each 1600mm apart (not 1500mm, just did the maths:rolleyes: ). So basically a 400 - 1600 - 1600 - 1600 - 400 configuration.

Prefitting the stirrups to the bearers and then fastening one end of the bearers to the wall made getting levels a breeze. I have 6 beams and 25 posts so I called one of those small concrete trucks and took 0.8m3 of concrete to fill my post holes, best labour saver tip I can give you. You have much fewer holes so you could probably mix your own but they do small loads and save heaps of time not to mention the back.

I've attached your diagram as it might look using similar construction methods to me.

I've realised my attachment didn't turn out so good so I'm trying again here.

Also thinking about it some more you could have the layout you are looking for by spacing your bears like this:
300 - 1100 - 1100 - 1100 - 1100 - 1100 - 300
which covers the 6100 width of your house nicely and is still safely within the joist span requirements of 90x45 joists (which are between 1200-1500mm depending what you read). The joists will happily cantilever the 300mm provided they are continuous span.

regards
Flats

Ben, 90*45 F8 treated pine joists at 450 centres (which you will need for the flooring width) will span 1500 single span if you want to sit them between the bearers & 1800 continuous if you've got the height (to span over 3 bearers.)
2/90*45 f8 treated pine bearers will span 1500 - i.e. 100 stump + 1500 + 100 stump = total 1700. Make sense ? The bearer can also overhang the stump up to 400 ( if the backspan is 1500)
The short width part of the deck will need 2 stumps - 1 at the house & 1 at edge but out from doorway you're going to need 3 stumps or deeper bearers.
I'd be inclined to go for the 3 bearers outside the door area anyway if only for the extra traffic load - it's only 2 or 3 extra stumps (couple of slabs of coldies)

Hey guys - thanks a million for the tips. Peter, you're dead right about the bearers near the door - I've taken your advice and will up the dimension accordingly (I have about 100mm extra clearance at that end).

I think I have my shopping list for the timber yard all sorted now, so will order up the timber this week.

One other quick question - how much canterlever can I expect from 19mm tongue and groove. I imagine it would need to be less than 100mm?

Now I just have to decide what to use as stumps....and start digging. So extra holes means more beer for me...

I'll try and remember to post some pics as I go.

Cheers

Ben