How much space are you putting in between the interior room wood framed top plate and the InsulDeck flooring? There is a "creep" factor to the concrete floor and that gap is needed so that the floor doesn't start crushing your interior wood frame walls.

A very good question.  That is something that I thought about, looked into a little, but hadn't asked the engineer or the subs about (but probably should).

I know we are doing double 2x4 at 16" OC for bracing with the interior walls.  I know the long term creep can be a issue, and the engineer designed the floors to keep it at a minimum.  From what I had read, the double 2x4's should have an axial bearing capacity of somewhere between 2400-8000 pounds (depending on the horizontal bracing and web site you look at).

If we went with the lower number (2400), that comes out to a little over 40psi compression between the top plate and concrete above.  My thought was that the 2" (or thicker) type VIII EPS will deform a fair amount at that PSI, absorbing some (if not most) of the long-term deflection.  I don't have exact numbers there, so I'll go ahead and ask my engineer and check with the framing and ICF subs to determine if they have further accounted for creep with this design.

I'd definitely appreciate any feedback or thoughts from those who has an opinion on this issue.

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I wasn't aware of the rotation count on the concrete trucks.  I hope the concrete company/drivers are aware of the issue, but will check the concrete out a little closer for any signs of incomplete mixing.

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I know the concrete will include fly ash and pea gravel.  I'll post other specs when I find out.  I'm not the expert, so I'll leave the exact concrete specs up to the engineer and ICF sub. 

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I'll try to post some additional detailed pics a little later this week.

Thanks for all the feedback.

Fly ash concrete is as strong or stronger than 100% Portland Cement mixes. Generally, you have to ask to get the fly ash content increased, particularly in residential. Many homeowners have heard that it is "bad".

I hope the concrete company/drivers are aware of the issue

They are, but everyone forgets to do something once in a while, particularly if they aren't accustomed to a short transit time. ;-) Everyone can see a poor mix when it is coming down the chute, but when you have the pumper hooked up and the mixer dumping it into the pump hopper, there is often only one or two people observing at that point and bad mix can go into the pump and deep down into the forms before anyone "notices" it.

We made our first wall pour on Tuesday, and everything went well. All the walls look straight and I think the concrete was well consolidated. They have started prepping for the Insuldeck.

We have a combination of ICF for the house and all the garage walls, and a number of formed concrete arches (non ICF) that go around the back side of the house to create a covered porch. They took down the wood forms on the columns and non-ICF arches and I was happy with the consolidation.

The walls were well braced, and the braces did go all the way to the top.

A look at the garage with some exposed steel in a column on the left.

A picture of the bottom of a window opening.

There are a total of 5 concrete columns on the first floor that help to hold up the insuldeck. The remainder of the house is supported by the ICF walls.

A picture of the garage wall and the beginning of the covered porch.

A view of the back of the house.

A look down a portion of the covered porch.

The front of the house.

There was a total of 130 yards of concrete in the 1st floor walls and arches. The first insuldeck pour will be about the same.

We are getting ready for the first Insuldeck pour.  Here are a few updated pics.

Looks very well designed and executed. Love the vertical columns and horizontal concrete reinforced beams. Looking forward to the view from the tower...

The insuldeck pour went without any problems and we are just about ready to pour the 2nd floor walls. 

Has anyone here done direct vent fireplaces through ICF walls?  I'm gessing the ICF foam may need to be removed a certain distance from the vent pipe going through the wall.  How is this usually done or are there any detailed drawings out there?

Thanks.

Posted By nd96 on 03 Apr 2013 02:21 AM
The insuldeck pour went without any problems and we are just about ready to pour the 2nd floor walls. 

Has anyone here done direct vent fireplaces through ICF walls?  I'm gessing the ICF foam may need to be removed a certain distance from the vent pipe going through the wall.  How is this usually done or are there any detailed drawings out there?

Thanks.

The code in most places is that the flue must be kept at least 2" away from the foam. If you contact Nudura they should have a detail and recommendation on how to pull this off.

As you noted, you don't want the hot flue vent pipe melting/burning away the foam within the wall. EPS foam will begin to soften at 170F and will melt around 180F+. Trust me, that flue will see temps of above 400F. When I shot thermals of my natural gas fireplace, I was getting those readings from the flue area.

I would contact Nudura and go from there. You don't want to have problems later on with melted foam in the wall.

You may be able to leave the foam if you use a class A triple wall pipe. As Lbear indicated, always best to communicate/coordinate with the product OEMs...wall and fireplace.

Posted By nd96 on 03 Apr 2013 02:21 AM
Has anyone here done direct vent fireplaces through ICF walls?  I'm gessing the ICF foam may need to be removed a certain distance from the vent pipe going through the wall.  How is this usually done or are there any detailed drawings out there?

Manufacturers of vent pipes will specify the required distance from combustibles.

For the Duravent vent pipe for my wood pellets stoves it is 1". I put a 6" pipe through the foam on the underside of the roof deck and the vent pipe inside that, with about 1" space. Works good.

I found details from the fireplace manufacturer. They recommend 1" around the pipe to any combustable materials. I think I might want a little more for EPS. I'd be a little concerned about the EPS starting to soften, then melt or drip onto the pipe (if it gets that hot). I'll check with my fireplace installer and ICF sub/rep to see what they say.

Posted By nd96 on 04 Apr 2013 06:07 AM
I found details from the fireplace manufacturer. They recommend 1" around the pipe to any combustable materials. I think I might want a little more for EPS. I'd be a little concerned about the EPS starting to soften, then melt or drip onto the pipe (if it gets that hot). I'll check with my fireplace installer and ICF sub/rep to see what they say.

I would feel better with 2" and that is code in most counties. Check with your building department or they might make you redo it, which is not fun with concrete.

What you will want to do, even with a 2" gap between the flue and EPS, is to thermally protect the EPS from the 400F+ flue heat. Whether it's high temp fiberglass batts (not paper faced) or some other material, you have to keep the 400F+ temps from permeating to the foam.

Don't forget make up air with a tight ICF home. Even with natural gas fireplaces, they are still consuming interior oxygen and create a pressure effect. You don't want to create a negative pressure which can cause back drafts and carbon monoxide to channel back into the home.

Posted By Lbear on 04 Apr 2013 06:32 AM

What you will want to do, even with a 2" gap between the flue and EPS, is to thermally protect the EPS from the 400F+ flue heat. Whether it's high temp fiberglass batts (not paper faced) or some other material, you have to keep the 400F+ temps from permeating to the foam.

400°? Single wall pipe, yes. Double and triple wall and insulated vent pipe, no way. Barely too hot to put one's hand on it. The 6" pipe around my 4" vent barely gets warm, no where near warm enough to soften foam.

nd96 - if its a direct vent f.p. , it probably has a coaxial vent system. That is, the exhaust gas goes out the middle pipe and the combustion air comes in the outside pipe. It would be the cold outside pipe that is in close proximity with your foam. Just follow the f.p. instructions for all clearances. Also, the kit probably comes with plates for both sides of the wall assembly. These are normally sealed to the pipe with high temperature caulking.

dmaceld has it right. Any pipe or assemble that reaches 400ºf would require 18" of clearance not 2" or 4". Single wall vent pipes are not allowed in building assembles. All natural gas would require a "B" vent unless they are high eff. which may use plastic. Always follow the instructions!

Thats what my thermal readings showed on my natural gas FP. According to online info, 400F - 800F are common natural gas flue exhaust temps. Wood burning FP stated temps of up to 2,000F. I shot the thermal temps on the inside and outside flue. Since the wall is sealed and finished I couldnt get in wall temp readings.

Flue Temps PDF

Posted By Lbear on 04 Apr 2013 11:20 AM
Thats what my thermal readings showed on my natural gas FP. According to online info, 400F - 800F are common natural gas flue exhaust temps. Wood burning FP stated temps of up to 2,000F. I shot the thermal temps on the inside and outside flue. Since the wall is sealed and finished I couldnt get in wall temp readings.

Of course natural gas will reach those temps. Just like your barbecue. We are not talking about the inside of the flue. Thats why different class vents are required for different appliances. A wood stove/fireplace has to account for chimney fires hence a "A" class chimney. A gas fired standard efficiency appliance will need a "B" vent and a high efficiency appliance may only require plastic. The one thing they all have in common is that you can put your hand on the outside of the flue when the appliance is a full bore without burning it.

If you are reading the outside of a insulated flue and getting those temps, you have three choices. Get a new gun. Recalibrate to account for emissivity. Call the fire department.

Posted By FBBP on 04 Apr 2013 10:24 AM
nd96 - if its a direct vent f.p. , it probably has a coaxial vent system. That is, the exhaust gas goes out the middle pipe and the combustion air comes in the outside pipe. It would be the cold outside pipe that is in close proximity with your foam. Just follow the f.p. instructions for all clearances. Also, the kit probably comes with plates for both sides of the wall assembly. These are normally sealed to the pipe with high temperature caulking.

Yes it is the "coaxial" vent with the hot exhaust pipe completely surrounded by the cooler incoming air.  I'm sure that does significantly reduce the exterior temp of the pipe.  But I guess the exact maximum temp is dependent on a lot of other variables like the rate of air flow, BTU of the fireplace, diameter and length of the vent, etc.  I know the vent size on the fireplaces I have picked out is 8" external diameter. 

I think I'd feel better with a 2" clearance, but I will see what the fireplace install company recommends and exactly what materials they bring out for the job.

Thanks for all the input.





The ICF sub poured the 2nd floor walls today.  It was a bit cool and muddy, but otherwise went well. 

Just the attic floor, 3' attic knee wall, and 16' tower left to do in insuldeck/ICF.  Then it is on to the rest of the construction process.

Posted By nd96 on 05 Apr 2013 12:05 AM

Yes it is the "coaxial" vent with the hot exhaust pipe completely surrounded by the cooler incoming air.  I'm sure that does significantly reduce the exterior temp of the pipe.  But I guess the exact maximum temp is dependent on a lot of other variables like the rate of air flow, BTU of the fireplace, diameter and length of the vent, etc.  I know the vent size on the fireplaces I have picked out is 8" external diameter. 

I think I'd feel better with a 2" clearance, but I will see what the fireplace install company recommends and exactly what materials they bring out for the job.

Thanks for all the input.

I think that pipe may very well be zero clearance because the outer pipe will be incoming air temp. What's the inner pipe diameter, 5"? Is your fireplace wood or gas? If gas, that pipe may be larger than recommended by the fireplace installation instructions. You want enough velocity in the exhaust air to avoid cooling below dew point at the exit and to provide a good draft. Believe it or not, but there is such a thing as too big when it comes to flue pipes.

Just for my understanding. With that flue design, if I understand what is being stated here, it operates like this:

The outgoing flue exhaust gas temperatures (which can be 400F or hotter) is cooled by the outside air temperature (let's say 40F) coming in through the flue. The 2 differentiating temperatures are separated by 2" of space between the hot exhaust gas and the cooler exterior air, and is being channeled through a flue which is made out of aluminum or steel, which is highly conductive, as with any metal.

The above process, which is almost like an HRV/ERV in the sense that it is "conditioning" the exhaust air by cooling it with exterior incoming air. The above design and process is able to take that 400F exhaust gas temperature and cool it to well below 140F by simple convection?

I am not trying to be condescending, I just find it amazing that it can drop the temperature by 260F while a HRV/ERV working at 90% efficiency taking 70F interior air and 30F exterior air, can only condition the incoming air to around 55F through the heat exchanger.

When I did my thermal readings over the winter (my laser thermal gun is accurate) on my direct vent gas fireplace it showed very high temperature readings at the flue interior base and exterior flue temperatures were in the 400F range. I can tell you that the builder on my home DID NOT put foam anywhere near the flue and it was basically wood framed in and a 4" gap between the flue and wood framing was left. No foam and no insulation. Not saying that it was done the best way, but that is what the spec home builders are doing when they do a direct vent FP on a wood frame home.

Posted By Lbear on 05 Apr 2013 02:47 AM
Just for my understanding. With that flue design, if I understand what is being stated here, it operates like this:

The outgoing flue exhaust gas temperatures (which can be 400F or hotter) is cooled by the outside air temperature (let's say 40F) coming in through the flue. The 2 differentiating temperatures are separated by 2" of space between the hot exhaust gas and the cooler exterior air, and is being channeled through a flue which is made out of aluminum or steel, which is highly conductive, as with any metal.

The above process, which is almost like an HRV/ERV in the sense that it is "conditioning" the exhaust air by cooling it with exterior incoming air. The above design and process is able to take that 400F exhaust gas temperature and cool it to well below 140F by simple convection?

I am not trying to be condescending, I just find it amazing that it can drop the temperature by 260F while a HRV/ERV working at 90% efficiency taking 70F interior air and 30F exterior air, can only condition the incoming air to around 55F through the heat exchanger.

When I did my thermal readings over the winter (my laser thermal gun is accurate) on my direct vent gas fireplace it showed very high temperature readings at the flue interior base and exterior flue temperatures were in the 400F range. I can tell you that the builder on my home DID NOT put foam anywhere near the flue and it was basically wood framed in and a 4" gap between the flue and wood framing was left. No foam and no insulation. Not saying that it was done the best way, but that is what the spec home builders are doing when they do a direct vent FP on a wood frame home.

The flue gas temps are not 400º. These are "reasonably" efficient fireplaces. The gas is burnt in the bottom of the box. The box acts as the primary heat exchanger which will drop the temps considerably. That is where the convection heat from the fireplace comes from.

There is no "space" between the in and the out.The pipes will not be aluminum.

Prior to the gas valve opening, the flue fan must prove air flow. It is not convection.