Question.. I started building my house in 03 using nudrua ICF, 8" in basement and 6" on main level and moved in in 06. The last couple days have been very cold here and I was hearing a muffled noise like someone was shooting a gun outside. It was around 10*. I went outside and didn't hear any gunshots and came in and still heard the occasional gunshot. I didn't hear any this morning. It had gotten down to minus 1 and warmed up to a balmy 14. It's cooling now and at 11* and I just heard 2 more shot. I think it's coming from the walls. Has any of you heard of this before or know what is going on? dana a

You may have trapped water someplace in the wall assembly. And with the low temps, it's freezing and probably cracking the surface of the concrete when it expands.

This is kinda similar to why trees explode in the winter.

What is your roof structure made of? SIPS are sometimes known to crack and pop due to temperature changes. What about your roofing material? Metal roofing can also crack and pop due to thermal expansion/contraction.

The roof is made of trusses on 2 foot centers then 5/8 OSB with asphalt shingles. I don't know what SIPS are.

I don't see how water could get in there but I suppose it's possible.. Thanks for the reply.

It's not water. We have had these stories here for some time, but they are usually new builds that are still drying. It could be that the cold is shrinking the building. The foam tends to bind. It's the only answer I have but, but not water.

Just a guess, but it may have more to do with the humidity than the temp (lower temp = dryer air). This can cause shrinkage/expansion of the wood (floor system, interior walls, roof). Pressure is created at connection points which eventually reaches a point where it POPS to alleviate this pressure. This does not cause any damage to the structure as wood is very good at shrinking/expanding repeatedly without losing structural strength. I would bet its the wood popping, not the ICF, but I could be wrong (first time for everything... )

Our temps have been very similar, and for a number of winters in the past too. Never heard anything like it!
ICFBdr might be on to something--what have your indoor relative humidity reading been lately?

I hope that is all it is. I didn't think it would be water as I have the rebar where it's supposed to be. I'd hate to think the place is crumbling apart

Are you sure the sound is coming from the exterior ICF walls? You indicated that you have trusses. Are you knowledgeable about truss uplift?

Truss Uplift Info

Did you use slotted anchor plates and truss clips to attach your interior wall top plates to the trusses? Did you hold back fastening the ceiling drywall at least 18” from the interior wall top plates? Are you seeing any drywall cracking? Thought here is that you may be hearing popping drywall fasteners. Truss uplift can lift entire interior walls off the floor if not addressed properly.

We have never experienced any noise coming from our ICF walls, but we don’t see the extreme cold temperatures that you see either. I will also say that you are in the temperature range where the ICF concrete temperature will reach the water freezing point. Water condensation can occur in concrete voids under the right humidity and temperature conditions. However, if you properly vibrated the concrete during the pour you should not have any significant voids in the concrete.

I hope that is all it is. I didn't think it would be water as I have the rebar where it's supposed to be. I'd hate to think the place is crumbling apart. The lowest humidity over night was 27% at 6* and currently 30% at 24*. I'm not sure but I think it was at 18% on Sunday. Both days I heard the popping somewhere around 6PM.

Don't stress about water INSIDE your ICF freezing and popping the concrete apart. Look at a driveway/sidewalk. This is concrete entirely exposed to water and going through extensive freeze/thaw cycles (even more when salt is used for de-icing!). If freezing water could split apart reinforced concrete my driveway would be reduced to gravel within the first year. Again - you will have little/no water in your ICF concrete. I would also be surprised if it made it to freezing point at the temp's you listed.

Keep an eye out for drywall cracks - as mentioned, this is the best telltale sign of truss uplift, shifting, etc.

The center of an ICF concrete core will reach 32F when you have steady state indoor and exterior temperatures of 68F and –4F respectively. The exterior section of an ICF concrete core will reach 32F at exterior temperatures even warmer than –4F. While I think it is extremely unlikely that freezing and expanding water in voids is causing this noise, this isn’t impossible either. The noise is more likely coming from popping fasteners used to fasten the drywall or interior walls to the trusses...or so I think...

Metal siding can also pop. My previous house had steel siding that would pop during temp changes, like when the sun first hits it for a bit.

We recently had some -20 f weather and we heard some loud cracking, popping sounds. Our house is all ICF exterior walls, ICF second floor system, wood truss roof (48' span) and steel studs with Mgo board on interior walls. Could be a lot of things, all of which expansion and contraction.