Post frame vs foundation

[LD1]

I maybe changing the design of the building I am planning for this spring. Looking for some feedback.

I am considering doing a 6 row block foundation instead of post-frame. I like the idea of having a few rows of block inside the building around the base. Seems it would be alot better for hosing down and cleanup, as well as lots more fire resistant when cutting, welding, and grinding out there.

I still want to go with steel siding and OSB interior. But what is the best way to construct the walls ontop of the block. I have never seen a metal siding building in person that had a block foundation, so not sure what the common method is.

Right now, I am thinking 2x6 studs on 2' centers with sheathing on the outside to attach the metal to. And trusses on 4' centers with conventional 2x4 purlins for roofing.

So some questions. Is the sheathing required? or does metal siding offer enough shear protection? And if I dont need sheathing, I would have to do something different to attach the metal to, as 36" spans of metal dont work out with 2' or 16" OC studs. So possibly running purlins outside the studs like a typical post frame? Would that offer enough lateral strength without the sheathing?

What about setting "posts" comprised of 3 2x6's on top of the block wall every 8-12' or so and building up like a post frame? 8 or 12' OC trusses would save money on the roof system, but will a block wall handle the less distributed loads of 40' span trusses?

So far, what I have calculated is only about $200 more on the 40x72 building to go block. Still factoring in other variables, but on a building this size, if block foundation is gonna be no more than ~$1000 more, I think I will go that route. I dont want to be worried about fires, or rotting out the inside from hosing out because I wanted to save $1000 on a $25k building.

 

[roadhunter]

We bought a pole barn kit 2 winters ago and are just now getting around to putting it up. The owner decided to pour a regular foundation instead of setting the posts in the ground. They welded up some brackets and are just using the same posts but putting them on top of the slab. It should work fine but IMO it will need quite a bit for extra bracing. I'll try to get some pics the next time I'm out there.

 

[Cat_Driver]

I think it would be easier to just place a "barrier" of block, poured concrete, steel sheeting etc. in front of the traditional wall build.
Building on top of block is less strong than building directly for a solid foundation.
Also you can soak the wood inside with fire retardant to further safety. Fire retardant comes in five gallon buckets and it's pretty cheap, and cheap insurance for any wood in a structure.

Why you need a strong foundation

 

[LD1]

I think it would be easier to just place a "barrier" of block, poured concrete, steel sheeting etc. in front of the traditional wall build.

Not looking to do what is easier. Looking to do what is best within reasonable cost.

Building on top of block is less strong than building directly for a solid foundation.

Are you saying that a post-frame construction method is stronger than typical house construction? And if that is the case, why arent houses built post-frame style instead of walls ontop of block foundations or basements?

 

[fordmantpw]

Our shop is built on a solid concrete foundation that sticks up 12-18" above the concrete floor. Then, the 2x6 walls (2' center IIRC) are attached to the top of the foundation walls. 2x4 perlins are run across the wall to attach the tin to. Trusses are 2x6 on 4' center with a 40' span. The shop at our other house was built the same way and it was great for hosing it out.

 

[Egon]

Are there any code requirements?

The stud wall will require lateral bracing of some type.
Wind loading will be a factor.
Also, wall to joist may require bracing.
Seeing as you will not have a continuous wall there may be design issues there.
You can run a special row of top blocks that can be filled with concrete and rebar and plate connections.
Can you check with your materials supplier for proper design?

Sorry that I've no answerers but 50 year old stuff may have changed for today.

 

[LD1]

So far, here is what I have figured:

For post frame build:
12' OC posts 18' long, set on 2' diameter concrete pads in bottom of hole
12' OC trusses
2x6 wall girts, laid horizontal and flush with both inside and outside of posts
2x8 treated band board
2x6 purlins in saddle hangers
And additional 2x4 and 2x6 lumber between 12' OC trusses to attach interior ceiling to
Liner panel around perimeter inside building

Total cost for that framework: $6802

For block foundation:
8.5 yds concrete foundation
942 block
22 bags mortar mix
4-ton sand
treated 2x8 sill plate
2x6 walls
OSB sheating
headers to clear 12' doors on eave ends
4' OC trusses and 2x4 purlins

Total cost: $7163

There are some things that I havent calculated on the block yet. Rebar for foundation. Filled cores with anchor bolts. But there are also some savings that I havent calculated yet. With 2 row of block above grade, It cuts out 16" of insualtion all the way around, probably shorten the metal by 12" all the way around, and with the inside wall being 8" smaller, will save a tad on he concrete floor too. A 40x40x4" pad is 19.75yds.
A 38'8"x38'8"x4" pad is 18.45yds. Surprising but shaving 8" off all the way around saves about 1-1/4yd of concrete....

 

[LD1]

Are there any code requirements?

The stud wall will require lateral bracing of some type.
Wind loading will be a factor.
Also, wall to joist may require bracing.
Seeing as you will not have a continuous wall there may be design issues there.
You can run a special row of top blocks that can be filled with concrete and rebar and plate connections.
Can you check with your materials supplier for proper design?

Sorry that I've no answerers but 50 year old stuff may have changed for today.

No code requirements, not much wind loads. No hurricane area.

I dont think there is any issue with design as it is exactly how houses are built. Unless I explore other options like I mentioned. (posts on the block instead of stud-wall).

 

[LD1]

Our shop is built on a solid concrete foundation that sticks up 12-18" above the concrete floor. Then, the 2x6 walls (2' center IIRC) are attached to the top of the foundation walls. 2x4 perlins are run across the wall to attach the tin to. Trusses are 2x6 on 4' center with a 40' span. The shop at our other house was built the same way and it was great for hosing it out.

I though about using 2x4 purlins outside the studwall, but surprising when I calculated it, there wasnt much savings. OSB sheathing was $600. 2x4's on 2' centers totaled $550. I supposed I could cheat them out to 30" centers and save a bit, but I think a stud wall relys alot on the sheathing for lateral stiffness?

 

[fordmantpw]

I though about using 2x4 purlins outside the studwall, but surprising when I calculated it, there wasnt much savings. OSB sheathing was $600. 2x4's on 2' centers totaled $550. I supposed I could cheat them out to 30" centers and save a bit, but I think a stud wall relys alot on the sheathing for lateral stiffness?

The tin will provide the lateral stiffness necessary once it's all screwed together. I was thinking my perlins in the wall were at 4' centers, but don't remember for sure.

 

[s219]

There is a lot of inherent shear strength in a pole-barn construction with the ends of the posts in the ground 3-4 feet, and diagonal braces between poles. With a framed wall, the shear strength will have to come from sheathing. There would be some shear strength from metal siding, but much more limited and probably more failure prone in certain scenarios, so I'd want OSB if it were my building. I doubt siding alone would pass code, which is some guidance to go by whether or not you need to get approvals/inspections.

When my dad had a construction business after he got out of homebuilding, he did a lot of contract jobs building guard shacks and portable buildings for gov agencies and military bases. For those, we'd use OSB over a 2x4 or 2x6 framed wall, and then screw steel siding over the top of the OSB (I do remember a lot of customers wanted steel siding with wood-grain texture and graphics, which always struck me as funny). The siding would usually get tacked on temporarily with an air stapler using 1/4" staples to hold in place, and then someone would come around behind that and drive 1" metal screws through the siding into the OSB. Don't remember the screw spacing, but it was on the order of 16-24" or so. It was a very strong combination and pretty much lifetime construction. The buildings would be subjected to a lot of moving loads from cranes, forklifts, construction equipment, etc, and were solid as heck. So that's one data point in favor of steel siding over OSB.

My current garage and last garage were framed walls directly on top of a block foundation, and I see no reason you couldn't use that for a shop/barn construction. Put j-anchors in the top of the wall to secure the sill (pressure treated) and bottom wall plate and you're good to go. There is a lot of new structural hardware that can help anchor the walls for the best results -- for instance angle plates that tie into the j-anchors and then run up a wall stud 12" and fasten with 8-10 1/4" structural screws. If the masonry work isn't an issue in terms of labor/cost, I think wall framing over block is a great way to go.

I can see how a few rows of block would be better for hosing out the place, but that's not something I'd want to do, since it introduces a lot of moisture into your work area that will take a while to go away. In the meantime it's all around your tools, materials, equipment, etc. I hosed out my workshop once, and never again.

There would certainly be a fire benefit to having some block on the wall, but unless it goes up pretty high, I'd say it will be marginal. There is so much other stuff that could still catch on fire. I'd probably do 1-2 courses of block above floor level, and then start the framed walls. Put up some scrap metal, hardi panel, drywall, etc in an area that might see a lot of sparks from welding/cutting/etc.

I don't think there is a real benefit to putting posts on top of a block wall -- you'd still need a ton of bracing and/or sheathing to get any shear strength, and I can't think of reliable ways to attach posts to block walls (reinforced solid concrete walls, yes, but not block walls).

 

[LD1]

There is a lot of inherent shear strength in a pole-barn construction with the ends of the posts in the ground 3-4 feet, and diagonal braces between poles. With a framed wall, the shear strength will have to come from sheathing. There would be some shear strength from metal siding, but much more limited and probably more failure prone in certain scenarios, so I'd want OSB if it were my building. I doubt siding alone would pass code, which is some guidance to go by whether or not you need to get approvals/inspections.

When my dad had a construction business after he got out of homebuilding, he did a lot of contract jobs building guard shacks and portable buildings for gov agencies and military bases. For those, we'd use OSB over a 2x4 or 2x6 framed wall, and then screw steel siding over the top of the OSB (I do remember a lot of customers wanted steel siding with wood-grain texture and graphics, which always struck me as funny). The siding would usually get tacked on temporarily with an air stapler using 1/4" staples to hold in place, and then someone would come around behind that and drive 1" metal screws through the siding into the OSB. Don't remember the screw spacing, but it was on the order of 16-24" or so. It was a very strong combination and pretty much lifetime construction. The buildings would be subjected to a lot of moving loads from cranes, forklifts, construction equipment, etc, and were solid as heck. So that's one data point in favor of steel siding over OSB.

My current garage and last garage were framed walls directly on top of a block foundation, and I see no reason you couldn't use that for a shop/barn construction. Put j-anchors in the top of the wall to secure the sill (pressure treated) and bottom wall plate and you're good to go. There is a lot of new structural hardware that can help anchor the walls for the best results -- for instance angle plates that tie into the j-anchors and then run up a wall stud 12" and fasten with 8-10 1/4" structural screws. If the masonry work isn't an issue in terms of labor/cost, I think wall framing over block is a great way to go.

I can see how a few rows of block would be better for hosing out the place, but that's not something I'd want to do, since it introduces a lot of moisture into your work area that will take a while to go away. In the meantime it's all around your tools, materials, equipment, etc. I hosed out my workshop once, and never again.

There would certainly be a fire benefit to having some block on the wall, but unless it goes up pretty high, I'd say it will be marginal. There is so much other stuff that could still catch on fire. I'd probably do 1-2 courses of block above floor level, and then start the framed walls. Put up some scrap metal, hardi panel, drywall, etc in an area that might see a lot of sparks from welding/cutting/etc.

I don't think there is a real benefit to putting posts on top of a block wall -- you'd still need a ton of bracing and/or sheathing to get any shear strength, and I can't think of reliable ways to attach posts to block walls (reinforced solid concrete walls, yes, but not block walls).

Thanks for the reply.

My thought about putting posts on top of the block wall was all cost related. And would it be cheaper to do so, and space the trusses back to 8' or 12' OC and still have an acceptable level of strength. But further analyzing it, a simple stud wall on 24" centers with 4 OC trusses seems to be the cheapest.

As to the added cost of the foundation, that will be minimal. Have a backhoe, and block experience. So spending 1200 on block and mortar vs 1200 on 6x6 posts is a wash. Its my labor either way as nothing will need hired out. Which is where I think the majority of the cost difference comes from when reading online about how much more $$$ stick built is.

Hosing out is a non issue. Did it in my old garage that was OSB. But had to keep it away from the walls. With a wood burner and heated shop with a central floor drain, it dries quickly. Just dont want to have to worry when nearing the edges and getting them wet. As to fire and sparks, I think 2 row of exposed block will work. The cutting and welding is always done several feet away from a wall, as wall space is always tied up with tool boxes, shelving, air compressor, parts washer, etc. Just worried about the ones that roll across the floor and come to a rest at the walls edge.

I have been doing a ton more reading online, and 99% of what I read claims the 2 biggest benefits of post-frame is strength, and cheaper.

Well, cost is figuring the same with me doing the labor either way. So it really comes down to strength. The touted claim of having several posts 4' in the ground keepig it from blowing away.....with proper fastening of the wall to the block, I think it will be just as strong. And likewise, proper fastening of the roof structure to the wall.

So, while a post frame "may" be a little stronger, with never testing the limits of a foundation in my area, a post frame may be overkill. And if we do happen to have a once in a lifetime tornado roll through and destroy the garage, thats what I pay insurance for.

So for the time being, Here is what I am planning:
2' wide 6" thick footer with rebar
6 course 8" block wall
treated 2x8 GC rated sill plate. Properly anchored to filled cores in the block. (need to check into how many/how far apart these need to be.
Then I will pour the concrete floor to have a nice place to work
Pre-built wall sections with 2x6's stood up and anchored to the foundation
7/16 OSB sheathing all the way around
4' OC trusses w/2x4 purlins laid flat
Metal roofing and siding

Then will work on interior insulation, OSB walls, surface mounted wiring in conduit, lighting, etc

Now just waiting on the weather to break in a few months so I can dig a footer.

 

[KennyG]

Are screws into OSB adequate for holding siding? I'm pretty sure it's not for roofing, but maybe OK for siding. I like the idea of 2x4's mainly because you can use a good treated grade board, but maybe that doesn't matter much if your slab is well above grade.

 

[LD1]

Are screws into OSB adequate for holding siding? I'm pretty sure it's not for roofing, but maybe OK for siding. I like the idea of 2x4's mainly because you can use a good treated grade board, but maybe that doesn't matter much if your slab is well above grade.

Not sure on the holding. I would think it would be sufficient. I have seen alot of houses go up with OSB sheathing for the roof with metal down on top.

Not sure 2x4's will give the lateral stiffness I need. Maybe with them + the steel??

No need to worry about a treated gradeboard. Site is flat, and will be 2 rows of block above ground topped with a treated board. The OSB wont come into contact with the ground or the block. And will extend the metal 6" or so down the block to eliminate the chance of rain blowing up under the metal siding and getting at the OSB

 

[tman1020]

Post frame buildings are very difficult to beat price wise and strength especially if you are going tall. That being said concrete in the ground is always better than wood in my book. You mentioned about doing your footing 6 inches thickI would recommend eight. And I know you said you have experience laying block but I am much more fond of poured walls. If you do decide to go stick framing in your walls I was curious why you were using two by sixes instead of two by fours? Is it because of height I didn't catch how tall you plan to build. On your truss spacing I preferred to go 2 foot on center and use half-inch OSB and then just use a standard shingled roof rather than steel and purlins. Some of the benefits that I like are that it minimizes condensation and is much quieter on uninsulated buildings. But if you're insulating won't make much of a difference either way.

 

[LD1]

Post frame buildings are very difficult to beat price wise and strength especially if you are going tall. That being said concrete in the ground is always better than wood in my book. You mentioned about doing your footing 6 inches thickI would recommend eight. And I know you said you have experience laying block but I am much more fond of poured walls. If you do decide to go stick framing in your walls I was curious why you were using two by sixes instead of two by fours? Is it because of height I didn't catch how tall you plan to build. On your truss spacing I preferred to go 2 foot on center and use half-inch OSB and then just use a standard shingled roof rather than steel and purlins. Some of the benefits that I like are that it minimizes condensation and is much quieter on uninsulated buildings. But if you're insulating won't make much of a difference either way.

Good questions.

I like poured walls too, but the added cost of forming and material make it hard to justify for just a single story garage.

6"x 24 is what I am shooting for and will likely be thicker in areas. 6" will be the minimum. And 2' because I have a 2' bucket on the hoe. Dads 2-story with full block wall basement called for 8" x 24, So I think 6 should be sufficient. But will certainly research footer specs before committing.

2x6 walls is for strenght AND insulation. I want a well insulated shop, Especially with going 12-14' high ceilings.

4' OC trusses is strictly a cost thing. They are $126 per truss and require 19. 2' OC trusses are only $20 less and need 37 of them. So it makes it a few grand more expensive. And my preference is metal roof. I dont like shingles. So given metal roof, and no drywall underneath, I really dont see the need to go 2' trusses.

I am actually considering laying more block. Going 4' above ground that way I can use 8' lumber for the walls instead of 12'. 8' lumber is cheaper per ft than 12' lumber. Will just have to look at how much more laying a few more courses of block will be. And also have to consider how it will look from the exterior, and less insulating value for the bottom 4' of wall......decisions decisions..

 

[tman1020]

Yes the uninsulated block will be a heat sink. I no longer use 2x6 walls just for insulation. Instead I use 2x4 and use premium cellulose blown in. It gives me effective r17 and almost no air filtration and only costs about 10 percent more installed than if I install r 13 batts myself. Plus I save the difference between the 2x4 & 2x6. Don't forget you will need at least 2 runs of #4 re-bar in those footings. I use 3 in 24 wide. Remember the last place you want to skimp it's on the foundation it will be the hardest to repair if you have a problem. Sounds like it's going to be a very nice building whichever way you go.

 

[Billrog]

If your sheeting the interior walls with OSB why not just strap the out side with 1x4 to attach the metal to they'll hold roofing bolts much better than OSB . Your interior shting. will give you all the necessary strength combined with the exterior metal.

 

[LD1]

If your sheeting the interior walls with OSB why not just strap the out side with 1x4 to attach the metal to they'll hold roofing bolts much better than OSB . Your interior shting. will give you all the necessary strength combined with the exterior metal.

good thought, but I wasnt planning on sheathing ALL of the inside.

The building will be 40x72. I will build a wall 40' deep into the building and have a 40x40 section that is insulated and heated. The back 32' is gonna be unfinished for now. Just tractor and equipment storage

 

[s219]

So for the time being, Here is what I am planning:
2' wide 6" thick footer with rebar
6 course 8" block wall
treated 2x8 GC rated sill plate. Properly anchored to filled cores in the block. (need to check into how many/how far apart these need to be.
Then I will pour the concrete floor to have a nice place to work
Pre-built wall sections with 2x6's stood up and anchored to the foundation
7/16 OSB sheathing all the way around
4' OC trusses w/2x4 purlins laid flat
Metal roofing and siding

Then will work on interior insulation, OSB walls, surface mounted wiring in conduit, lighting, etc

Now just waiting on the weather to break in a few months so I can dig a footer.

Sounds like a good plan to me, especially if you are comfortable laying block -- that is a big advantage being able to do your own masonry. As much as I appreciate the simplicity and fast progress of pole barn construction, and despite having used it on my barn, having a full on block foundation is preferable to me. If I had to do it again, I would have made my stick-on-block workshop bigger and detached from our home, and not built a separate pole barn.