vent and water absorber question

I have few questions.

I have 3 vents, 1 ½†from sink, 1 ½†from washer and 2†from toilet. Can I join all of them in the attic and have only one 2†coming out of the roof.

Are the water absorbers mandatory for washers? Do they need to be installed inside of the wall, or I can use those mounted on valves at washer valve/drain box? If in the wall, what’s the proper way to install.

Thank you Michal

Yes, you can combine all of the vents. Keep in mind though, that if they are separated a large distance, it may not be practical. Each vent has a maximum length and must have slope just like drains, to allow condensation to flow and not accumulate. The ultimate size of the vent going through the roof will depend on local codes and the number of fixture units to be vented. Those in northern climes where frost could be a problem need to make the part exiting the roof larger.

Unless you have water hammer issues, water hammer arrestors (water absorbers) are not mandatory. They are recommended for quick closing fixtures such as washers but their use is purely subjective.

vents

You can combine them, BUT, the code usually requires that the AREA of the pipe exiting the roof, or the aggregate areas if there are more than one, must equal the AREA of the incoming sewer line. For that reason, if this will be the only vent, you will probably have to start increasing the size as you combine the vents until you end up with a 3" or 4" pipe through the roof. And if you are in a freezing area, it will probably have to be increased further to either 4" or 5" as it goes through the roof.

Thanks guys,
The vents are within few feet. I The drains tap into 3†drain pipe which goes into main line. So what will be the proper size of the vent? I don’t live in freezing area. I’ll post some pictures later.
Michal

for a washing machine I used the sioux hammer arresters that screw in line with a hose. Mount them to the back of the washer. Then attach the hose to it. This suposedly helps protect the washer hoases as well.