Pardon me if I'm doing this wrong- 1st post on the forum.
Wow- I feel your pain! Ours is a 13 year old Heart modular- with exactly the same issues you described... and then some! Problem is, the company went defunct, and we aren't the original owner- so no warranty transfer on our issues. Nice. I was told not to waste my time. That a company in class action would end up paying next to nothing after several years of fighting.

Before I rant, I would first like to solicit opinions from other owners. I wonder if spray foam insulation may solve a few of the issues you will see below?
Any other suggestions would be appreciated as well! I would prefer not to chemically bomb the home, or spend a great fortune, but we do need a healthy home that we can enjoy.

To be fair, a lot of the issue is the install.
Where the siding meets the foundation is a 2" gap that the critters love. The top of the siding meeting the roof is the same. Under the house, gaps that you can see daylight through.
These numerous gaps (top & bottom) have allowed us to play host to mice, bats, red, grey, & even black squirrels. I have tried every means of elimination. We can hear them scratch and thump in the ceiling, walls, & floors all hours of the day & night. This was going on with 3 cats killing them! I have fear they may chew wires & burn the house. I'm sure they have destroyed what little insulation there was.
We put plastic on all the windows & the wind still blows through. No window closes completely or can lock in place. None were installed properly.
There is frost on the inside of the walls.
I added a picture of the roof we replaced this past year. We crawled up to clean the leaves out of the gutters, turns out it was shingle grit filling them- not leaves.
It was unfortunate that our family did the work and didn't know enough to add step flashing -now we have leaks, too. We will be removing 3 sections this spring.
The roof has no crawlspace or access to insulate, so we have 6 foot icicles & 8" ice damns around the entire roof edge as well.
The plumbing has no access panels & no standard parts. It's all factory built. So there are no shut offs in emergency. To do any work, have to shut off the main then cut the pipe. Later, can replace properly with a shutoff and screw on.
There are many more issues... but I need to go make supper. Thank you for your patience with my rant. Please let me know if you have had similar experiences.

Wow, my sympathy to you people!

I don't have near the issues posted, although the subfloor is not as good as it should be . You have put luan board down to put new flooring in. My home is 25 years old.

I have a 1973 Wausau home that nothing has ever been done to except roof shingles and vinyl floor in bathroom. There is some water that leaks in on the basement floor. Other than that, nothing. At this point we will be doing a complete remodel, as after 50 years, it needs new windows etc etc

Wendy, out of curiosity, where is that home (generally) licated? We’re looking at a Wausau home from that general period, and outside of some exterior siding issues, it seems to be in good repair.

We feel your pain. We thought Wausau Homes 2as a good company. The contractor that did our home has not completed work, the work he did do is horrible. Took off with funds that should had paid sub contractors. The list goes on. Spoke with Wausau homes not really getting anywhere. Can't afford to get an attorney as we need whatever.money we have left to complete and correct the crap job contractor did not finish. Oh and by the way 4 days after the contractor installed a fireplace, we had a fire. Wausau should have monitored this contractor better. The fireplace was.for natural.gas only with no conversion. We had LP. Wish I would had done my homework better as I would never have went with Wausau Homes.

Hu, sorry for the huge delay, but our 1973 Wausau home is in Bayfield Wi. Just now starting our big remodel. The other thing is even the siding is in good shape, super solid and I am free-cycling it rather than landfill. Have had 1 mouse get in it in over 20 years. But again, water in the basement because it's on a hill.

Wausau Homes is only responsible for the panelized walls - nothing else that the GC is responsible for doing. Our GC was TERRIBLE and made the build a nightmare. Check out the GC and get references!