I am planning on building a small deck on the side of my house where there is no door or window. The level of the deck is below the top of the basement, so I need to drill through the concrete for the ledger board. However, because there is no door, I am thinking about just building the deck as freestanding without attaching it to the house. One downside that I can think of is that the deck edge might drift relative to the house, making it look crooked. Is this is a problem? What are the downsides of making the deck freestanding?
The big drawback is that your footings aren't done right or don't hold up well and you have a deck that slants a little compared to the house. You could end up with a little dip or a lip when you walk out the door. This may take one year or 30 years or 100 years. If you don't have a ledger it will happen. If you are building on very solid ground maybe your concerns aren't as bad but eventually these two things will look like they don't belong together.
Builders like doing it this way because as long as the footings are good the deck should generally stay where it is compared to the house for a few years. Also what do you do if your deck is slanted 5 degrees or is pulled out from your house an inch or two. I really doubt there is a monetary remedy for slight frustration. And the flip side for builders is attaching. Messing up your structure or allowing water into your structure is not only very quantifiable but could also come back to hunt them soon after a build. So $$$ will dictate that a builder wouldn't attach to your house if it were their choice - especially if they are subcontracting it out.
Flashing a house for the ledger isn't rocket science. There should actually be flashing under and over the ledger. I have helped put up 5-6 decks, always used a ledger and never heard anyone have water issues. And these were just all put together neighborhood style - no pros. I can't imagine not using a ledge unless the deck was only a foot or two off the ground.
For your situation I could see going either way. The fact that you are going through concrete is actually good for waterproofing - concrete doesn't rot if you have an issue. But I do understand that you want it to be easy and without a window or door it would have to really go off course to look wrong.
Doing this has the advantage of not having to attach a ledger board to the house, which must be flashed carefully to keep water from getting in.
The big disadvantage is that you don't get stability of hooking to a big immovable house, so if the deck is a second-floor one, you will probably want more diagonal bracing on the posts to keep things stable. If it's a low deck, this probably doesn't matter.
So, no real reason not to do it detached. There are a number of builders who do it this way.