Can the Sandhyavandanam and the japam both performed outside the house - in the garden for instance. I find it more peaceful.
Yes, Sandhyavandanam can be performed both inside the house and outside of it. Some places, which are outside the house, like river banks and temples are considered as the very best places for performing Sandhya.
The following verse from Laghu Satatapa Smriti is quoted in the book "Nitya Karma Puja Prakash".
Griheshu tatsamA sandhyAm goshthe shataguna smritA |
NadyAm shatgunA proktA anantA shiva-sannidhau ||
If performance of SandhyA inside the house gives one unit merit, in the cowpen it gives 100-fold results, in the river banks 1 lakh-fold and infinite results are obtained from doing it in a Shiva temple.
Laghu Satatapa Smriti 114
Here is the PDF of Nitya Karma Puja Prakash. You can find the verse given in the 69th page of the book.
In the verse if you check one Shatguna is translated as 100 fold and the other Shatguna as one lakh fold. I think there might be some error in the Sanskrit verse.– RickrossAug 9, 2019 at 6:22
Sandhyavandanam are to be performed 3 times a day facing the direction of the Sun. Example If you are doing in Morning, you should face the Sun (East Direction) and if you are doing at Evening, you should face the West Direction.
As such, there is isn't pre-defined place for it, but logically doing that in open area like Garden/Terrace would help in getting more exposure to sun shine and fresh air.
4Welcome! Answers on this site should be backed up with proper sources. Please visit Guidelines for new users answering questions– The Destroyer ♦Aug 9, 2019 at 10:51
This answer doesn't really need any external sources for what is said in it. It is a fact that performing Sandhya three times a day and getting exposure when you sit in open area, you get exposure of Sunshine and fresh air. What proper source is needed to say you get Sun shine if sat in fresh air? It is pratyaksha Pramana. It is a fact like "Sun rises in the East" and regular ritual for those who perform. You just have to go and check and obvious. If you think it needs sources, specify which part needs citations. Still it is like spoon feeding. @TheD Aug 10, 2019 at 5:57