Pouring concrete in winter

[mldrenen]

I recently purchased a few acres, and had great hopes of building a small cabin before the winter set in.  As you can tell by the title of this thread, I'm woefully short of my goal. 

I have the holes dug for a concrete pier foundation, and was hoping to pour the footings this weekend, but the forecast calls for a high of 35 with a low in the 20's.  The Quickrete packaging says not to pour in temperatures below 50 degrees. 

I'm not terribly worried about the footings, because I figure that they are several feet below ground, and I can cover them with plastic to keep them warm (40's?) and frost-free.  My big concern is when I go to pour the actual piers.  I doubt that we'll have warm enough temps between now and April to get those poured correctly.

So......what does the collective wisdom of CP have to say about mixing and pouring concrete in cold temps? 

[mldrenen]

I thought I might mention that I plan on building a 10'x10' cabin, with 8 perimeter piers, 10' high walls, and a sleeping loft.  I've been told that 8 concrete piers is overkill, but I would rather over-build than under-build.  I want this cabin to last, as it will see many years of future use as a weekend retreat, home office, and guest house.

[dug]

Just poured my piers a few weeks ago with low temps in the 20's, but highs were more like 50 or better. I was nervous as heck and did a fair amount of research. Use more cement in your mix (creates more heat and speeds drying) and keep them covered. I used some of the insulation that will go in the house later. I know concrete has been successfully poured in lower temps than what you have now, but it certainly is not ideal.

[mldrenen]

Just poured my piers a few weeks ago with low temps in the 20's, but highs were more like 50 or better. I was nervous as heck and did a fair amount of research. Use more cement in your mix (creates more heat and speeds drying) and keep them covered. I used some of the insulation that will go in the house later. I know concrete has been successfully poured in lower temps than what you have now, but it certainly is not ideal.

Thanks for the tips.  Glad to hear that you didn't have any trouble.  I'm hoping that with a few extra precautionary measures and a pinch of luck, I can get the piers done in the next week or two.

[Squirl]

I made the decision to wait until spring.  I am looking to build a larger place, but I want it to last a while.  I have read that concrete does not last as well over time (crumbles) if poured below freezing.  I do not have any experience with pouring concrete in that type of weather and was just not willing to take the risk.  I have heard of contractors that say you can pour concrete all year with special preparations and others that shut down business because they don't want to risk their reputation.  Fifty degrees was too far from twenty for me.  I wouldn't worry as much if the high was close to the minimum temp, but 35 is only 3 degrees above freezing.  I would wait for more responses from more members with experience in below freezing pours.

[poppy]

Back in a former life, I was a concrete inspector and checked on concrete after winter pours.

The key thing is adequate insulation to prevent the surface temperature from going below a critical temp.  Unfortunately, that was over 40 years ago and I don't remember the target temp. but I'm sure it is easily available.

Remember that concrete generates its own heat as it cures; that's why winter pouring is possible.

As a second thought, with such a small cabin, why not forget the concrete piers and do the type of foundation that is designed not to freeze.  With proper design and drainage it is possible.  That is easy to find also.

A third thought is to pour the bases in place and then use PT posts.

[MountainDon]

Concrete takes 28 days to reach maximum strength, and for that to happen it must retain moisture and must not freeze. At best freezing will result in surface flaking. It's true that concrete is exothermic as it cures, that is it gives off heat from the chemical reaction that cures the concrete. With a high of 35 and lows down to 20 you would definitely need to insulate them well to stand any chance of preventing a freeze, and allow the cure to take place. Even then my personal feeling is that it is not something I would do. I have seen the results of concrete poured here in the winter desert and it was not pretty.

[MountainDon]

As for the number of piers it would seem that 8 is overkill. Are they arranged 5 down each of the opposite sides that will be under the gable roof eves? What size beams do you plan on using?

Is this in an area subject to inspections?

[mldrenen]

Good points, Poppy.  I have considered pouring the bases and cutting the piers to just below ground level, then finishing the rest with PT lumber.  I'm not sure how that would work.

As for the types of foundations recommended in John's plans and utilized by nearly everyone on here, I just am not very familiar with them, and therefore thought a concrete pier foundation would be easier for me to construct.  Judging by the pictures I've seen on here, it seems that those foundation types are utilized in more flat and dry terrain than what I am working with (Berkshires, Massachusetts).

It's not too late in the game to change my mind.  I'd scrap the idea of using concrete if I was convinced that I could build something just as stable and economical.  I'd really rather not wait until spring to get this thing built.

[mldrenen]

As or the number of piers it would seem that 8 is overkill. Are they arranged 5 down each of the opposite sides that will be under the gable roof eves? What size beams do you plan on using?

Is this in an area subject to inspections?

Four piers on the corners, four in between.  Each wall will be supported by 3 piers.  Initially I planned on just four at the corners, but was told that because of the downward force of my roof and loft that I should put three on the side walls.  Because of the loft and roof height, I was also planning on utilizing a ridge beam, and supporting it on the gable ends.  Therefore, I added the additional piers on those sides as well.

This area is subject to inspection, but I was told that any structure under 120 sq ft is exempt from permits and inspections.

[rwanders]

I have done many concrete pours in below freezing weather (even below zero at times) here in Alaska. Insulation is required and even heaters if very cold but it is definitely doable----it is not necessary, in most cases, to provide heat after 7 days curing time. By that time there is not enough "free water" present in the placement to cause any serious problems. The larger the pour mass is, the better, due to the heat supplied by the exothermic processes----i.e. slabs are more difficult to protect compared to thicker footings or columns. Most concrete suppliers can provide direction on protecting your pour while curing in cold weather. Do not be fearful----it can be done in your temperatures with some simple precautions.

[MountainDon]

Here are a few links of interest...

from Grace Construction Products, a PDF file

http://www.concretenetwork.com/cold-weather-concrete/curing.html

http://www.deeconcrete.com/concrete/coldweather.asp

Anything can be done if enough resources are used. My previous statement was meant to simply state that for me freezing weather concrete pouring requires more equipment and eort than I care to invest when all I have to do is wait a couple months at the most to get back to weather above 40 degrees. Not everyone is so fortunate. I may be spoiled. Yeah, no doubt I am. 

[poppy]

Here's another site that has tons of good info. on tiny house building.

http://tinyhouseblog.com/

A 100 sf cabin is indeed tiny and the foundation need not be a big deal.

I'm sure you have your own reasons for making it 10'x10' but that is unusual considering that standard building materials tend to be in 4' increments.

For 100 sf most folks would do 8'x12' for example. 

Also basic shed design might be in order for such a small cabin and one option for them is to build on PT skids and placed on a gravel bed.  If it needs to be raised higher then precast concrete blocks can be used under the skids.

If the gravel bed is properly drained then freezing is not an issue.

I wouldn't pour concrete piers for a 100 sf building even if it were the middle of the summer, but that's me.  For what it is worth I did use concrete piers for my 16'x16' cabin.

[mldrenen]

My previous statement was meant to simply state that for me freezing weather concrete pouring requires more equipment and eort than I care to invest when all I have to do is wait a couple months at the most to get back to weather above 40 degrees. Not everyone is so fortunate. I may be spoiled. Yeah, no doubt I am.  

Great information in those links.  Thank you.

I'm beginning to feel the same way as you do.  I want the foundation work to be quick, simple, and cheap.  I will be mixing and pouring it myself, and I'm not 100% confident in my abilities to keep the concrete warm enough to avoid any damage.

[mldrenen]

Here's another site that has tons of good info. on tiny house building.

http://tinyhouseblog.com/

I'm sure you have your own reasons for making it 10'x10' but that is unusual considering that standard building materials tend to be in 4' increments.

I read that blog at least once a week.  I love seeing the creativity and craftsmanship that goes into a lot of these tiny homes.

I don't have any particular reasons for choosing one size over another.  The idea of a square building seemed nice.  I was also inspired by these little houses:

http://vermonttinyhouses.com/

Ideally, I would like to have the cabin roughed in before the end of January.  It will serve as my "base camp" from which I can conduct the building of my actual house next summer.  This little building will store some tools, a small cook stove, food supplies, and be able to house a few bodies on weekends.

[mldrenen]

My next questions pertain to shallow gravel and precast concrete foundations, such as this one:

http://www.coyotecottage.com/cabin/cabinconstruction/foundation.htm

I had initially wanted to build something simple like that, but I wasn't able to find the materials (precast concrete piers) locally.  Which led to to assume that they are not suitable to my locale.

For those that have used this type of system, where did you find your supplies?  Have you had any trouble with heaving/settling?  How deep is the frost line where you built?  How deep did lay the gravel footing?

[Redoverfarm]

Generally you would be OK with pouring in the Mid 30's.  The concrete will heat up as it cures and with a few hay bales placed around and over your pour they should cure enough so that the temps should not effect them.  By using the hay bales over and around you are essentially insulating that space.  The heat generated by the concrete will be trapped by the hay and they will cure enough that temps should not effect it after 24-48 hours.  If it is a real concern calcium can be added to the mix or an excellerator.

[MountainDon]

I don't have any particular reasons for choosing one size over another.  The idea of a square building seemed nice.  I was also inspired by these little houses:

A square house gives more square feet of floor space for the least amount or wall lengths.

10 x 10 =  100 sq ft and 40 linear feet of walls.
8 x 12 = 96 sq ft and 40 linear feet
Not a big difference on a small house.

As for building with multiples of 4 feet, tell that to my 15.75 x 30 foot cabin. I may be  but I had my reasons. 

[MountainDon]

  Which led to to assume that they are not suitable to my locale.

That sort of product is usually limited to a local geographic market because of transportation costs. That's most likely the reason you couldn't find them; nobody local is making them. With proper drainage and insulation that system is used successfully in areas with very cold freezes.

[poppy]

I'm in a cold climate and the pre-cast concrete piers are at the local Lowe's.  Some folks just use patio stones.  Or make your own with buckets in your garage.

I have read of a guy in the NE somewhere who used shallow based piers for his cabin, but I can't find the link.

[davidj]

Don't forget there are two sources of heat you can use to stop it freezing - the heat from the concrete cure and the heat from the ground.  If you can cover an area around the piers with insulation, as well as the piers themselves, you get to use the heat from the ground.  Even when it's going down to the 20s it doesn't need much insulation to stop the ground - and stuff in contact with the ground - from freezing, especially if you have an air barrier or two (i.e. tarps) along with something like hay or leaves.  It sounds crazy, but I bet you could even use snow to help keep it above freezing if you had some other insulation beneath the snow.  I used shredded bark, fir branches, a tarp and snow to prevent frost heave on my open foundation last year - worked great!

[Squirl]

I did a small 12x8 in upstate NY.  I did it those dimensions because there was less cutting plywood than a 10x10 because I was using hand tools.
http://countryplans.com/smf/index.php?topic=7305.0

I understand the 8 piers.  Almost no span table recommends a girder unsupported for a 10 ft span. So that would be three on the sides and every book I have ever read recommends a strait load trace down to the foundation with a ridge beam.  The simplest way would be to just add a pier in each center.  As you can see I used the precast piers for 4x4 pt posts for my shed.  I wasn't as worried about frost heave because there is no drywall/plaster and it is not a house.

There are a dozen ways to shave a cat.  I think that is how the expression goes.  From the home page.
http://countryplans.com/foundation/index.html

The point is usually to get the post below the frost line.  I assume for you in Mass. would be 4 ft.

You could use the same precast with concrete block method you showed earlier.  Just lower.  My understanding is you would fill it in with gravel.
Or if you or a friend has a basement, warehouse, or heated garage you can make many precast methods to pour and wouldn't have to worry.  I picked up a great book at a used book store for two dollars called Concrete Projects by popular science magazine.  I was just reading it a few days ago.

You could pour a footing with a Simpson bracket that many have used here and put a PT post up from that.

In the book I saw a method for making a foundation for a boat dock.  You could pour a base circle of concrete with a 1" steel pipe in the center and pour small circular "blocks" that will fit over the pipe and build it up like that.  If you wanted to be creative you could even create forms that were steadily decreasing in size so that in more evenly distributes load like the donuts on a stick children's toy.

Or if you have a lot of individuals, a heavy dolly, or heavy equipment you could precast a whole pier and drop it into place.  Be careful a 4ft 8" post with 16" footing should weigh around 300 lbs.

If I can think of any other methods I will let you know.

[mldrenen]

I'd like to thank everyone for all of the informative responses.  It gave me a lot to think about.  Here's what I wound up doing/deciding:

I placed rebar in the holes, exactly as shown in the second diagram, poured the footings and covered the entire work area with a tarp. 

http://countryplans.com/foundation/index.html

Once the footings are cured, I'll pour the piers and insulate them with straw and cover with tarps.