I recently purchased a condo unit in a new 3 storey 24 unit ICF condo building in Ontario.
Each unit is equipped with its own Johnson Controls propane furnace.
Both the furnace exhaust and air intake pipes  ( 2-3"diameter) for each unit extend to a flat area of the roof.
Due to ICF construction the furnaces do not operate for a long periods of time, in fact, even if the furnace in a particular unit is shut off, the temperature in a unit only drops to 15 or 16 degrees C in winter as long as there are furnaces operating elsewhere in the building.
There are no caps on the exhaust and intake pipes on the roof and they are open to the sky.
Several furnaces have shut off and refuse to start as ice caps sometimes form at the top of the pvc exhaust pipes.
Once the ice is removed the furnaces will start to operate.
Another problem is that several furnaces have shut down due to water entering the furnace.
Again they start once the water has been removed.
The builder is blaming the problem on the fact that in an ICF building the furnaces do not operate for long enough periods to keep the stacks free from moisture and freezing..
We have spoken with the design engineer and he will recommend either installing caps or 180 degree bends on the ends of the pipes.
The builder is planning to recommend residents keep their furnaces set at 20 - 22 degrees C, although a furnace shut down last weekend when set at 22.

Does anyone have any suggestions in addition to intalling caps?
ICF is meant to save energy and here is a case where residents are being asked to burn more!
Don 150

Even with a 180 degree bend at the cap they'll still be prone to frosting up from exhaust condensation freezing to the PVC.

Raising the temp a couple of degrees doesn't appreciably affect the duty cycle. No surprise that it doesn't really work. When it's -20C outdoors and 20C indoors that's a 40C delta. Bumping up to 22C indoors makes it a 42C delta, which would only increase the duty cycle by 5%. It doesn't take rocket science type math to figure this out.

Having a 180 degree bend on the combustion air intake would be worth it, to keep rain & snow from getting in.

The shorter the length of the venting run, the warmer the exiting exhaust is. A more likely solution (clearly not the easiest) would be to side-vent the furnaces fairly close to where they are installed. This has all sorts of clearances to windows/doors and other issues, but at least the exhaust would be at or above human body temp at the exit, with a lower propensity to frost up. When it's going up 10 meters inside 20-22C conditioned space, the surface area of the vent piping (and it's thermal mass that stagnates to well under 30C between burns) reduces the temperature of the exhaust along the way- it's a long skinny heat exchanger.

It's likely that the furnaces are ridiculously oversized for the heat loads and running less than 20% of the time even during the coldest weather, a common issue for multi-unit buildings even with conventional construction. It may be better to use air handlers running off the water heaters, which are probably still oversized for the space heating load, but not quite as much, and the duty cycle of a hot water + space heating solution would be higher, and thus less prone to icing up. In high performance buildings annual hot water heating energy usually exceeds the space heating energy use, which may even be the case here.

Blaming the ICF for the oversizing of the furnaces is pretty lame on the builder's part. It's up to the designers to come up with appropriately sized mechanical systems. While it's hard to find furnaces that run at the likely sub-20,000 BTU/hr design heat loads, hydronic air handlers or baseboard/radiator systems suitable for water heaters or hydronic can be sized appropriately for arbitrarily low heat loads. The heat load of an ICF condo building is still going to be more than half that of a code-min well constructed condo building, and even right-sized condensing equipment can run into frost-up issues with long vent stacks.

The design engineers should be able to tell you the calculated heat load of each individual residence (if they can't, they didn't do the job.) Compare that number to the output of the furnaces. If the furnace output is more than 2x the heat load figures it's not really great- if it's 4x it means the duty cycle never goes over 25%. While the efficiency of the furnaces can still be pretty good at 4x oversizing, it's lousy from a frost-up susceptibility point of view. It would not be unusual to see even more than 4x oversizing of hot air furnaces in condos, which is why hydronic solutions running off the water heater are often a better approach.

If you have pvc stacks it means you have high efficiency units. These should have condensate lines coming off the furnace at the start of the exhaust run. If they don't, that could be the problem.

In Ontario, these new construction units are covered under Tarion, also the intake and exhaust is specified in the installation manual for the heating unit. The TSSA over sees the proper installation of the fuel burning device.

If the builder is not acting quickly in these situations, a call to Tarion gets the ball rolling. If you know the HVAC contractors info, contact them, it should be on the gas line tag, if that doesn't resolve, carefully call the TSSA. I say carefully, because they will come and inspect (or re-inspect), if they find the install is incorrect they will red-tag and shut down the unit, leaving you with no heat, this can be very inconvenient for you, Tarion has systems in place to cover expenses (the hotel you will have to move to) while the repair takes place, but this only happens if the install was incorrect (outside what the mfg allows), if it is correct and failing, the expense will be on you, but the builder still has to make good on fixing the problem, even if that means having the mfg figure it out or replace it with a different unit within a reasonable time frame (reasonable being the unknown).

Very few HVAC designers have the ability to properly calc for ICF, it has been an issue since I began ICF and still continues, it is better, but not 100%

I can't remember ever seeing a high eff. unit venting through a roof in any project I have been involved with.

I would NOT fault the ICF. I would fault the design…but there likely wasn’t one. This was likely the result of a builder using a HVAC contractor who is very proficient in “catalog engineering”!