Deck Strength?

[Ron]

Last fall I added on to my deck in anticipation of getting a tub this spring. Well, the tubs almost here and I think I am getting cold feet as far as the deck strength goes. Was'nt nervous all winter but now I am. I thought it was designed adequately now I'm not sure. Surfing the net for information and examples isn't helping. Some stuff I find makes my deck feel inadequate, some makes me feel ok.

My basic design is:

Added new deck off from existing deck and screened in porch (actually 5 sided since it ties into existing deck at an approx 45 deg)

Ledgers are 2"X8"

New deck is roughly 13'x11' (not including angled section which adds a couple of feet)

Under the tub are 3 beams, each beam is doubled up 2"x8"

Beams are spaced apprx 3 1/2' apart (puts one beam at each end of the tub and one in the middle)

Beams supported by (9) 4x4's posts (3 each beam)

Beams lag bolted to sides of 4"x4"

4"x"4" posts on top of 8" diameter footings, 48" deep

Joists are 2"x8" 15"OC

The tub going on this is : HS Grande (I know,,, just had to get the biggest/heaviest)

Thanks for any insights. I have pics if anyone was interested.

Ron

[turbottt1]

We built a 12'x16' raised deck for our tub. [aprox.3' up] We installed a center beam [2x10] with 4 post divided equally. We then installed a post for each corner of the tub and tied them into the joist with 2x10. We also split the difference on each end and added a post tied to the joist. This was unneeded just worried about the same thing as you. Our spa holds 450 gals. and we have had 7 people in it at one time. There is no way our deck would give in. Now I assume you placed at least a 6" concrete footer under each post????????? Not dry bag and water , but a mixed concrete footer????????? Good luck Fyi Under your beams where you nailed to the post nail another support block this will help from the nails pulling out. Also make sure if you have a ledger board. That it is lagged real good to the house. If your still worried have your spa dealer come take a look. I know ours would be happy to help. steve

[hottub.pool_boy]

first- have the dealer look at it.

[Ron]

....Now I assume you placed at least a 6" concrete footer under each post????????? Not dry bag and water , but a mixed concrete footer????????? Good luck Fyi Under your beams where you nailed to the post nail another support block this will help from the nails pulling out. Also make sure if you have a ledger board. That it is lagged real good to the house. If your still worried have your spa dealer come take a look. I know ours would be happy to help. steve

Yes, under each 4x4 post is a footer 8" in diameter, 48" deep. 9 holes altogether, took me and my brother-in-law all day to dig them with a powered auger and get them poured! We started early and finished in the dark. And yes,,, it was mixed. We rented a power mixer.

Never thought about having the dealer take a look. Maybe I'll call them tomorrow. Is it common for them to evaluate decks?

[hottub.pool_boy]

yep. we want you to be safe.

[Ron]

yep. we want you to be safe.

And I just want to be able to stop worrying about this and be done with it. Need to get some sleep. Besides, my better half is getting real irritated with me

I sure hope it's worth it in the end.

[Roger]

Last fall I added on to my deck in anticipation of getting a tub this spring. Well, the tubs almost here and I think I am getting cold feet as far as the deck strength goes. Was'nt nervous all winter but now I am. I thought it was designed adequately now I'm not sure. Surfing the net for information and examples isn't helping. Some stuff I find makes my deck feel inadequate, some makes me feel ok.

My basic design is:

Added new deck off from existing deck and screened in porch (actually 5 sided since it ties into existing deck at an approx 45 deg)

Ledgers are 2"X8"

New deck is roughly 13'x11' (not including angled section which adds a couple of feet)

Under the tub are 3 beams, each beam is doubled up 2"x8"

Beams are spaced apprx 3 1/2' apart (puts one beam at each end of the tub and one in the middle)

Beams supported by (9) 4x4's posts (3 each beam)

Beams lag bolted to sides of 4"x4"

4"x"4" posts on top of 8" diameter footings, 48" deep

Joists are 2"x8" 15"OC

The tub going on this is : HS Grande (I know,,, just had to get the biggest/heaviest)

Thanks for any insights. I have pics if anyone was interested.

Ron

The only problem I read out of this and other than it this would be fine. Lag bolting the beams to the post is not the proper way to do this. The post either need to be notched or set under the beams. Or there is brackets available that put the weight on the post from the top and not on the shear point of the lag bolts.

[turbottt1]

Talk about irritate your better half. I built our house ,our barn, and everthing else, but when it came to this deck I built it, tore it apart added post twice. Ever try digging post holes when ya have joist 16" on center in your way??? Yes the wife did help dig. [ for a short time then she started calling me names which I won't repeat] lol!!! Yes as much as it pains me to agree with roger [ lol!!!] he is right about the shear points. Thats why we added the extra blocking under our beams. good luck stop worrying and yes the spa will be worth more than any pain the deck causes you. steve]

[StanW]

Last fall I added on to my deck in anticipation of getting a tub this spring. Well, the tubs almost here and I think I am getting cold feet as far as the deck strength goes. Was'nt nervous all winter but now I am. I thought it was designed adequately now I'm not sure. Surfing the net for information and examples isn't helping. Some stuff I find makes my deck feel inadequate, some makes me feel ok.

My basic design is:

Added new deck off from existing deck and screened in porch (actually 5 sided since it ties into existing deck at an approx 45 deg)

Ledgers are 2"X8"

New deck is roughly 13'x11' (not including angled section which adds a couple of feet)

Under the tub are 3 beams, each beam is doubled up 2"x8"

Beams are spaced apprx 3 1/2' apart (puts one beam at each end of the tub and one in the middle)

Beams supported by (9) 4x4's posts (3 each beam)

Beams lag bolted to sides of 4"x4"

4"x"4" posts on top of 8" diameter footings, 48" deep

Joists are 2"x8" 15"OC

The tub going on this is : HS Grande (I know,,, just had to get the biggest/heaviest)

Thanks for any insights. I have pics if anyone was interested.

Ron

Another option you have is to goes to Lowes website. They have an on-line deck designer. If you put in your information, it'll lay out what their design. It may not be exactly like yours, but it will show you what they recommend (with stress calculations). My "gut feel" is yours is more than adequately designed. I put a six person tub in last Fall with 2x8s and one double beam under the spa. I spaced the joists 12" since I ran the decking boards diagonally. It's working fine. If we had an earthquake or a tornado, I'd get under the deck, as the safest place to be. Just kidding. Good luck with your deck and enjoy your spa.

[Ron]

Talk about irritate your better half. I built our house ,our barn, and everthing else, but when it came to this deck I built it, tore it apart added post twice. Ever try digging post holes when ya have joist 16" on center in your way??? Yes the wife did help dig. [ for a short time then she started calling me names which I won't repeat] lol!!! Yes as much as it pains me to agree with roger [ lol!!!] he is right about the shear points. Thats why we added the extra blocking under our beams. good luck stop worrying and yes the spa will be worth more than any pain the deck causes you. steve]

Thanks for feeling my pain,,,

Yes, the sheer points are one of my big concerns. How did you add extra blocking under your beams?

I did try to look up sheer points for bolts. Only had minor luck. I found a source that said "most bolts have sheer points of 200lbs". With a 6,000lb tub (filled) the weight on each beam-post bolt would be 166lbs, but this doesn't count the weight of the deck.

[Roger]

Thanks for feeling my pain,,,

Yes, the sheer points are one of my big concerns. How did you add extra blocking under your beams?

I did try to look up sheer points for bolts. Only had minor luck. I found a source that said "most bolts have sheer points of 200lbs". With a 6,000lb tub (filled) the weight on each beam-post bolt would be 166lbs, but this doesn't count the weight of the deck.

Or the people or anything else that's out there. Temporarily support the deck and cut the post's to fit under the headers. If the space is to wide for the post use a 6x6 block on top of the 4x4. Or a simple 2x block just wide enough to cover the space between the headers. Preferable a 1.5 inch notch on both sides of the 4x4 leaving only a half inch in the center with both header beams set in these notches on each side of the 4x4. Then carriage bolt through both beams and the post with 1 or 2 bolts just to hold it together.

Oh and Steve...I don't feel the love brother......LOL

But if your going to leave it Ron, take out the lag bolts and replace them with 4 predrilled 1/2 inch carriage bolts with nuts and washers, all the way through, see if you can find a grade 5 minumum. And maybe SS or grade 8 preferably, galvinized.

[turbottt1]

Roger come on!!!!! There's nothing but love.LOL!!!! The way roger described is the proper way. What I did was right under my beams where they cross the post I cut 2x10 aprox. 8" long and corner nailed with 16 penny galv. twist nails and bolted completely through the bocks and post. steve

[Ron]

Or the people or anything else that's out there. Temporarily support the deck and cut the post's to fit under the headers. If the space is to wide for the post use a 6x6 block on top of the 4x4. Or a simple 2x block just wide enough to cover the space between the headers. Preferable a 1.5 inch notch on both sides of the 4x4 leaving only a half inch in the center with both header beams set in these notches on each side of the 4x4. Then carriage bolt through both beams and the post with 1 or 2 bolts just to hold it together.

Oh and Steve...I don't feel the love brother......LOL

But if your going to leave it Ron, take out the lag bolts and replace them with 4 predrilled 1/2 inch carriage bolts with nuts and washers, all the way through, see if you can find a grade 5 minumum. And maybe SS or grade 8 preferably, galvinized.

Thanks Roger. I think I'm tired from the lack of sleep,, but I'm not sure I follow this. Do you mean to cut (notch) the 4x4 that is already there? In the first part what do you mean by "header"?

Also, if I went with your 2nd suggestion, there would be (4) 1/2 holes in each 4x4 for the carriage bolts. Is this too many holes in a 4x4? Any chances of it splitting? Probably can't be worse than the 4 holes I have for the lag bolts (I think I used 3/8", not all the way through of course). The 1/2 holes for the carriage bolts would be clean at least.

But if your going to leave it Ron, take out the lag bolts and replace them with 4 predrilled 1/2 inch carriage bolts with nuts and washers, all the way through, see if you can find a grade 5 minumum. And maybe SS or grade 8 preferably, galvinized.

Oh, forgot. Would SS be better than galvinized? How does grade 8 compare stregth wise to SS? I've found both but the galvinized does seem to list the grade (that I have found).

[Roger]

Oh, forgot. Would SS be better than galvinized? How does grade 8 compare stregth wise to SS? I've found both but the galvinized does seem to list the grade (that I have found).

SS for the consumer dosen't always list the grade but is probably suffiecient for your aplication. Galvinized will also be fine. With a 1/2 inch carriage bolt you will be spreading the load from above through the 4x4 across the carriage bolts surface 4 times. With a lag bolt you are creating a shear point at the seam between the beam (header) and the post. The downward force on the header pushes the pointed end of the lag up and the head end down. With a carriege bolt through the entire works both ends of the bolt are forced down to spread the load through the post. You should be able to spread the carriage bolt holes 6 inches apart up and down and 2-3 inches apart side to side. For that matter use 3 in a diagnol line from top to bottom.

Yes I meant that if it was possible take the exsisting posts and remove them notch them on both sides 1.5 inches in and 7.5 inches deep from the top this will leave you 1/2 inch in the middle at the top of the post. Sandwich your header (beams) in these notches and then one carriage bolt (but I use 2) the entire thing together. But you would have to temporarily support your deck and remove your exsising header (beams) to acomplish this. If your beams are only toe nailed to your joists this may be doable. But not an easy job from the underside.

[grahamtasia]

If your deck is rated out at 115 to 120 lbs per square inch where the Grandee will be, you will be fine. Good luck!

[Guzz]

If your deck is rated out at 115 to 120 lbs per square inch where the Grandee will be, you will be fine. Good luck!

The Grandee is one of my favourite spas, you'll love it, congratulations.

[Ron]

SS for the consumer dosen't always list the grade but is probably suffiecient for your aplication. Galvinized will also be fine. With a 1/2 inch carriage bolt you will be spreading the load from above through the 4x4 across the carriage bolts surface 4 times. With a lag bolt you are creating a shear point at the seam between the beam (header) and the post. The downward force on the header pushes the pointed end of the lag up and the head end down. With a carriege bolt through the entire works both ends of the bolt are forced down to spread the load through the post. You should be able to spread the carriage bolt holes 6 inches apart up and down and 2-3 inches apart side to side. For that matter use 3 in a diagnol line from top to bottom.

Yes I meant that if it was possible take the exsisting posts and remove them notch them on both sides 1.5 inches in and 7.5 inches deep from the top this will leave you 1/2 inch in the middle at the top of the post. Sandwich your header (beams) in these notches and then one carriage bolt (but I use 2) the entire thing together. But you would have to temporarily support your deck and remove your exsising header (beams) to acomplish this. If your beams are only toe nailed to your joists this may be doable. But not an easy job from the underside.

Awesome explanations Roger, thanks. I really like the idea of notching the post, but not practical. The beams farthest away from the house doable, the middle beam maybe, the beams closest to the house very tough. The deck is really close to the ground there. IIRC, the post is not much higher than the 2x8's. But, replacing the lags with carriage bolts shouldn't be too bad.

Here's what I am thinking. Since I already have 4 holes in each post for the lags (2 on each side opposing diagonals) I will replace 2 of the lags with carriage bolts. Basically taking out the lags (one at a time) and drilling all the way through with a long 1/2" bit and bolting in the carriage. This will leave 2 diagonal carriage bolts on one side and 2 diagonal lags on the other side (opposing each other of course). This way I don't have to drill any additional holes in the posts (just run 2 of the holes through to the other side). Sound strong enough?

I will probably go with the galvinized. Haven't found any SS carriage bolts locally.

If your deck is rated out at 115 to 120 lbs per square inch where the Grandee will be, you will be fine. Good luck!

Problem is, I am not sure what the deck is rated. Calculating that is way beyond me. But, I did find a website that looks like they have some awesome load calculators. It is a pay feature but only $9.95 for a 2 month password.

[Roger]

Problem is, I am not sure what the deck is rated. Calculating that is way beyond me. But, I did find a website that looks like they have some awesome load calculators. It is a pay feature but only $9.95 for a 2 month password.

Rock and Roll Ron....it should be fine (place disclaimer here) I can't remember what size joists and on what spacing or what dimension decking you were using?

I have the same type of structure under my deck. The posts closest to the house if you look at them are 3 inches high, theres actualy 9.5 inches sandwitched between the beams but you can't see it. I buily me lower deck to support a HT but decided after that the space was to valuable to me so changed the placement of the tub next to the deck instead. Get yourself a long bell hanger bit 1/4 inch to drill a pilot all the way through. Then you can use a standered 1/2 bit from either side. The long bit will be much cheaper and will be something you will need in your tools box for other things. Like drilling through the walls of your house and stuff.

[grahamtasia]

Looks like you have a nice big deck to offer your friends and family!!

[Roger]

Looks like you have a nice big deck to offer your friends and family!!

Yea where the table is was where the Tub was going to go but we found the space to valuble so we plunked it alongside.

[Ron]

Rock and Roll Ron....it should be fine (place disclaimer here) I can't remember what size joists and on what spacing or what dimension decking you were using?

I have the same type of structure under my deck. The posts closest to the house if you look at them are 3 inches high, theres actualy 9.5 inches sandwitched between the beams but you can't see it. I buily me lower deck to support a HT but decided after that the space was to valuable to me so changed the placement of the tub next to the deck instead. Get yourself a long bell hanger bit 1/4 inch to drill a pilot all the way through. Then you can use a standered 1/2 bit from either side. The long bit will be much cheaper and will be something you will need in your tools box for other things. Like drilling through the walls of your house and stuff.

Got some good news today. Long story short, I have a neighbor who is an architect, but more of a designer. But,,, he works with structural guys. The structural guy did some calculations of my design. The calcs were way, way beyond me. Simply said, he shows that I exceed what I need. I do need to replace the lags with some carriage bolts. Will have that done buy Monday.

When,,,,, I have the delivery of my hot tub at 10:00AM!!!!!!!!!!!!!!!!!!!!!!!! Still need to schedule the electrician,,,, always something,,,, lol.

[Guzz]

Got some good news today. Long story short, I have a neighbor who is an architect, but more of a designer. But,,, he works with structural guys. The structural guy did some calculations of my design. The calcs were way, way beyond me. Simply said, he shows that I exceed what I need. I do need to replace the lags with some carriage bolts. Will have that done buy Monday.

When,,,,, I have the delivery of my hot tub at 10:00AM!!!!!!!!!!!!!!!!!!!!!!!! Still need to schedule the electrician,,,, always something,,,, lol.

Looks great, spatopia is on its way.

[Ron]

Looks great, spatopia is on its way.

Ah, yes. I need some spatopia.

Well, got the lag bolts replaced with 1/2" galv carriage bolts, what a pain, crawling under a low deck with rocks under my back. Had to remove some decking just to get to some of the posts. Didn't even get on my computer for 2 days, wow I'm exhausted.

But, I am as set as I can be for my 10:00AM delivery tomorrow. And yes, still have a million worries. But, I think my deck will be fine (crossing fingers).

I am going to call my electrician tomorrow. Bad news is,,, it is supposed to rain all week.

Starting to cut the cedar for my pergola/privacy fence, with a lot of luck, maybe we will get to take a dip next weekend.