Heating half the slab

[bfarroo]

I'm planning on building a new workshop / storage building. The current plan is for a 50x100 sectioning 50x50 as a workshop and 50x50 as cold storage. I want to install infloor heating and want to know if this is a bad idea? I would think I would at least want some sort of insulation between the two areas in the floor but don't know if there would be any other issues with this setup? I will probably put insulation and tubing through the whole slab just in case I ever decide to heat the entire building. I'm sure this will be the first of many question so I thank you in advance for your time.

 

[BadgerBoilerMN]

This is a common practice.

First a proper heat load. The heat load determined by measuring the square feet, room height, windows and doors. The R-value for each is put into a dedicated software program.

Each area of the country has a different outdoor design temperature. You decide what the inside design temperature will be. For instance, in your home the inside design temperature would likely be 70°F. We design most residential garages 50°F.

The difference between inside and outside design temperatures is one of the main components of a proper heat loss. This information along with your local heat source and fuels help determine the best way to invest in insulation both below the slab and in walls, doors and ceiling.

The colder the climate and/or the more expensive the available fuel, the more you want to insulate and the more time you want to spend on the heat source and controls.

It is a good idea to tube any slab as the PEX tubing and insulation is least of any radiant floor heating system and hard to do after the cement is poured. We call it "Radiant Floor Ready"®.

You will insulate below the slab with solid foam "XPS" 25# is accepted for commercial type installations. Both the heated and unheated areas will be insulated with a thermal break between the two. I normally will not require a thermal break between an office and a shop.

We place a 6mil vapor barrier on compacted soil, the foam, staple PEX to foam and add flat wire or rebar before pouring cement.

Now I will let the other weigh in but remember the basics.

This is what a proper Manual 'J' heat analysis looks like.

 

[bfarroo]

OK, then what is typically used for the thermal break? would it just be another piece of insulation installed vertically between the two halves? One inch or two inch? Currently I'm going to focus on getting the building up which means I need to decide on the floor. Where do most purchase their XPS Insulation from? I would imagine sourcing it from a distributor would be much more cost effective than buying it from Home Depot. Also what is the difference between using wire mesh and rebar in the concrete? It seems like the rebar is stronger but at a cost and labor increase. Also do most do a monolithic pour, or put footings in first and then the floor second. Most of the info I see on putting the vertical insulation around the outer edge show it inside the footings, but if the pour is monolithic then this would be impossible right? would the insulation then go on the outside?

 

[Red Goat]

Where do most purchase their XPS Insulation from? I would imagine sourcing it from a distributor would be much more cost effective than buying it from Home Depot

I just purchased 80 4'x8' sheets of 2" formular 250 (XPS). I checked all the insulation wholesalers and my neighbor (who is a concrete contractor) checked with his supplier, and none of them could beat Home Depots price. Go figure!!

 

[BadgerBoilerMN]

2" in Green Bay, the slab is a radiator, you wouldn't have a radiator exposed to the outside.

 

[Jackfre]

For the thermal break you can use the insulation. With the insulation on edge attach a 1 1/2 square piece to it at whatever height you decide and you can then drop an appropriately sized 2x6, 8, diamond plate or whatever you decide to match the grade.

...And what Badger said!

 

[bfarroo]

OK I understand needing/wanting insulation under and around the entire slab. My question is what the process would be if pouring the entire slab at once? Would the forms be setup 4 inches wider to accommodate the foam adding 2 inches on each side and the foam added along side the form before the pour? Or would the vertical foam be placed inside the forms and braced to be held in place during the pour? Adding the spacer to the insulation between the sections for the top plate is a good idea also. Some Diamond plate would be nice between the two sections.

 

[bfarroo]

I'm looking to get the floor ready to pour this spring and still don't have some of my questions answered completely. The two concrete contractors I talked to say they typically pour the slab as one piece(or two halves depending on the size) leaving thicker edges to support the building load but not a traditional foundation. I can't find any specific information on how to place the insulation to get a good thermal separation between the inside and outside with this type of pour. I find conflicting information on using the foam under the load bearing section of the concrete. Any other suggestions on placing the insulation?

 

[finn]

My garage in the UP has a thermal break to separate the heated / cold sections of the floor. The break looks like a vertical piece of foam board (~1") that is flush with the floor surface. I assume there are some sort of pins below the surface which were used to hold the foam in place during the pour, or perhaps they were pulled after the pour as part of the cement finishing process

The contractor warned me that it may be sort of a pain if I eventually want to roll things across this filler, and he was right.

Eventually I will construct a wall over the break and activate the heat

 

[BadgerBoilerMN]

You may not need a "Shock" thermal break, but it gives you and idea. This is a garage we did for two neighbors, one side heated and the other is not. Both share frost protected shallow foundation FPSP, but only one side has the perfect comfort of radiant floor heating.

http://www.ecobuild.co.uk/var/uploads/exhibitor/1959/v41xduwlyi.pdf

If you divide the slab with a 2" XPS thermal break, one side cold the other radiated.

 

[bfarroo]

How would the mini foundation section be insulated? Because it will all be poured at the same time it will be hard to keep the horizontal and vertical insulation next to each other. The foam would be laid across the floor section but when you get to the outside edges where it dips down for the last 12 inches or so before the forms is what I'm unclear about. Should I run the foam down into the lower area and up the sides of the form? I could insulate the outside but there will be the section around the entire building that won't be insulated.

 

[BadgerBoilerMN]

It is not a good idea to try to convey technical dimensions in writing over a blog and less wise to accept them.

This is what they make CAD drawings for. We can do it, but your local architect, builder or heating contractor should have had it done before breaking ground. Concrete contractors usually know precious little about insulation of any kind.

 

[CNGsaves]

So from July 2012 until now, the "50 ft x 100 ft" building with radiant heat floor has only gotten to point of whether to insulate the foundation or not??

Does OP have a budget for this??

OP are you trying to be your own General Contractor on this??

Has a builder been selected??

Have local and county rules on SIZE allowed, etc even been considered??

 

[rburke65]

There has to be a ton of info. and pictures on this forum if you do a search or just start reading.

 

[bfarroo]

I've spent all winter reading and researching. I plan on insulating the floor and foundation I just haven't found a lot of information on doing this specific type of slab. Everything I've found shows everyone pouring a foundation first then grading and installing the insulation inside across the floor and up the inside of the foundation. Then pouring the floor. I'm going to have to talk with the concrete guy and see how much more it would be to do the foundation first as this seems like the best way to go. I'm hoping to keep the building with concrete work under 60k. There are a few companies that I've been contacting on getting quotes for the building and concrete work. Some Offer everything while others just do the building. I'm planning on doing the infloor insulation and pex myself but the rest of the concrete work and building erection will be done by the contractors. The building will be put up on 4 acres in the country, There aren't any specific restrictions I have to worry about, I checked before purchasing the property, just have to pull the proper permits.

 

[hidollartoys]

Are you pouring a floor that is "slab on grade" or are you pouring a parameter footer first and then pouring a floor on top of the footer.

Google "insulated slab on grade", "insulated (concrete) foundation". This will start moving you in the proper direction.

In green bay I would suggest a parameter footer then a slab on top.

 

[danski0224]

I'm looking to get the floor ready to pour this spring and still don't have some of my questions answered completely. The two concrete contractors I talked to say they typically pour the slab as one piece(or two halves depending on the size) leaving thicker edges to support the building load but not a traditional foundation. I can't find any specific information on how to place the insulation to get a good thermal separation between the inside and outside with this type of pour. I find conflicting information on using the foam under the load bearing section of the concrete. Any other suggestions on placing the insulation?

If you can't get it to work with a "thickened slab", then use a different approach.

If you use a traditional frost line foundation, you can place your insulation correctly. An added benefit is being able to do something with the slab later without disturbing the foundation.

In some towns near me, once a residential garage goes over a certain size, monolithic pours even with a thickened edge are not allowed, and trench footings are also frowned upon. Local codes may dictate the construction- make sure you check.

You have to get the thermal break in there or else the radiant system will not work right.

 

[BadgerBoilerMN]

I think what you want is a frost protected shallow foundation. We use them whenever we can.

 

[bfarroo]

I'll do some research using that specific terminology and see what I can find. Thanks all for the help.