My last house, which was rather small (by midwestern American standards, anyway) had some interior walls that were very good at blocking 5GHz transmissions. (I never took them apart to look, but I suspect that some of them had plaster with metal lath as one or more layers.)

I started with one access point downstairs at the front (because that's where the cable modem lived) but it didn't work so well upstairs, at the back (diagonally) in the room I was using as an office.

So I added another access point upstairs at the back and that fixed it: Wifi became solid-enough both upstairs and down, and also covered the entire back yard, and also worked great for the neighbors when they asked if they could borrow a cup of Internet. It took some literal gymnastics in some very weird normally-unseen spaces to accomplish that run, but it got done. :)

As an side: It's interesting that being blocked by walls is also part of what makes 5GHz wifi so speedy indoors (in addition to having a lot more spectrum to use), for many [not all] people. By being attenuated so well by walls, the co-channel interference from the neighbors is reduced rather dramatically. With neighbors nearby, the RF environment tends to be a lot quieter at 2.4GHz than at 5GHz.

---

Present-day house is a bit lucky: All of the thirsty tech is on the first floor, and it's very simple to get ethernet cables routed 'round in the basement (it's all utility space). I was able to find enough pre-existing holes in the floor (from old cable TV installs and also floor-mounted outlets that have been removed and covered) that getting ethernet to every useful area of every first-floor room with tech in it was a very simple ordeal that did not require a drill. (Yeah, that means that there's a wire poking up through the floor behind the desk I'm sitting at right now instead of a tidy RJ45 receptacle on a wall plate with a nice port designation label. I'm over it; it works perfectly and inertia is a hell of a drug.)

But I'm not completely "lucky." The present house has aluminum siding and low-E windows. It's a great house that is amazingly inexpensive to heat and cool for how old it is, but it has aluminum siding and low-E windows and approximates a somewhat-leaky Faraday cage.

Thus, my cell phone barely works indoors, but it works great outside. And wifi barely works outside on the porch (front or back, doesn't matter), and really not at all beyond the porch (but things like my phone think that it should work, which is problematic).

I worked around that well-enough for the detached garage and back yard area by adding another access point in the garage, configured as a wireless repeater. Its advantage is that it has antennas that are optimized to work well, instead of some that are optimized to be very small (like those inside my phone, or my laptop). It's identical to the one inside the house and gets OK signal to/from the main AP, which it has a visual line-of-sight to through a couple of windows.

As an impromptu solution made from stuff I already had leftover from the last place, it works. I'm not winning any speed records with that remote access point... but it seems to be reliable, and reliability is good.

(Maybe some day I'll actually get around to upgrading the electricity to the garage to support some easy-to-access rooftop solar and/or car charging and/or welding and/or something, and when that trenching happens I'll also drop in some single-mode fiber. A single run of pre-terminated fiber is very cheap to buy, the "optics" at the endpoints are very inexpensive, and it is very safe with its essentially-absolute electrical isolation. It feels like overkill, but it's also once and done.)

As I understand, low-E reflects solar thermal infrared radiation (3-8 microns, 37-100 THz), while letting through visible light. I don't think it affects 5 GHz radio waves very much.

But yeah, it would be very satisfying to finally wire the house with ethernet.